Liverpool opened its Champions League title defense with a 2-0 loss at Napoli on Tuesday - the latest chapter in what is becoming an intense rivalry between the two attack-minded clubs after also meeting in last season's group phase.
Dries Mertens converted a penalty eight minutes from the end of an entertaining match after a foul by Andy Robertson on Jose Callejon.
Substitute Fernando Llorente then sealed it in stoppage time - a measure of revenge after playing on the Tottenham side that lost last season's final to Liverpool.
Last season, Napoli also beat Liverpool 1-0 at home before the English side won by the same score in England - denying Napoli a place in the knockout rounds.
Napoli and Salzburg, which routed Genk 6-2, took the early lead in Group E.
The atmosphere inside the newly renovated Stadio San Paolo was electric from the start as both sides attacked relentlessly from the opening whistle.
Napoli countered Liverpool's established attacking trio of Mohamed Salah, Roberto Firmino and Sadio Mané with a lineup featuring four forwards: Lorenzo Insigne and Jose Callejon on the wings surrounding Dries Mertens and Hirving Lozano.
Salah was on full sprint from kickoff but couldn't find a way past Napoli's center back Kalidou Koulibaly.
Liverpool goalkeeper Adrián - in his Champions League debut - denied Fabian Ruiz twice in one action before Lozano headed the second rebound into the net only to be whistled offside.
As dazzling as the offensive display was, the defense was just as impressive.
Joël Matip lunged to head away a cross intended for Lozano that seemed a sure goal then Ruiz sprinted back at the other end to intercept what would have been a tap-in for Salah.
The frantic pace continued, with Firmino heading just wide of the far post from a corner in the 44th.
Possession in the first half was split exactly 50-50.
The fireworks continued immediately after the break when Adrian hung in the air to deny a volley from Mertens with one hand at the far post.
There was a rare defensive mistake when Kostas Manolas gifted the ball to Salah in a great position but Napoli goalkeeper Alex Meret extended to glove the Egypt international's shot wide.
It was only in the last 15 minutes that the pace slowed, with both teams visibly exhausted on a warm evening.
Then Napoli found the breakthrough after Robertson was adjudged to have tripped Callejon in the area.
Adrián lunged to his left and got a hand on Mertens' penalty but couldn't stop it.
In the final minutes, Napoli fans' whistled so loud every time Liverpool had possession it was deafening, and it seemed to have an effect when Virgil van Dijk gifted the ball to Llorente, who rolled it past Adrián with ease.
Haaland hits hat trick as Salzburg beats Genk 6-2
Teenage striker Erling Braut Haaland introduced himself to the Champions League with a hat trick Tuesday as Salzburg hammered Genk 6-2.
The 19-year-old Norwegian gave Salzburg the lead in the second minute and added two more on counterattacks in the 34th and 45th. Haaland is the third-youngest player to score a Champions League hat trick after Raul in 1995 and Wayne Rooney in 2004.
The son of former Leeds and Manchester City player Alf-Inge Haaland, he attracted attention in May when he scored nine goals for Norway in an under-20 World Cup game against Honduras. Haaland has torn up Austrian competitions since joining in the summer from Norway's Molde, scoring 14 goals in eight league and cup games.
Hwang Hee-chan scored one goal and set up two more for Salzburg, which is playing in Europe's top club competition for the first time in 25 years and has U.S. coach Jesse Marsch in charge. Tuesday's game against Genk was the highest-scoring Champions League game since Paris Saint-Germain beat Celtic 7-1 in 2017.
The Austrian champion has not lost any of its last 19 European home games in deep runs through the Europa League knockout stages and has won nine of its last 10.
Belgian champion Genk has played in the Champions League group stage twice before, in 2002 and 2011, but has failed to win any of its 13 games to date.
Valencia beats Chelsea 1-0 in their Champions League opener
Rodrigo allowed Valencia to shake off a week of upheaval behind the scenes to clinch a 1-0 victory at Chelsea in the Champions League on Tuesday.
The opening victory in Group H came in only the second game in charge for Albert Celades since replacing Marcelino García Toral, who fell out with owner Peter Lim.
"This was a very hard fought win," Celades said through a translator. "The players showed a lot of commitment toward not just us the coaching staff but also to the club and fans."
The winning goal came from a player that Valencia nearly sold to Atletico Madrid in the summer transfer window. Rodrigo was left unchecked to race onto Daniel Parejo's free kick and volley into the net in the 74th minute at Stamford Bridge.
"I never felt alone, I always felt the players support," Celades said. "We have to make sure the noise outside doesn't affect us and work on things that will help us win matches."
Chelsea, meanwhile, has to work on its defense.
Rodrigo's strike was the 14th goal Chelsea has conceded in the seven games in all competitions since Frank Lampard took charge of the club he won the Champions League with as a player in 2012.
Chelsea fans were given a reason to cheer minutes after conceding, when a penalty was awarded after a VAR review determined that Fikayo Tomori's header hit the hand of Daniel Wass.
But the celebration was short-lived as Ross Barkley took the penalty —following a conversation with Jorginho and Willian— but it clipped the crossbar and flew over.
Chelsea suffered an early blow when Mason Mount limped off with an ankle injury after 15 minutes, having initially played on after being cut down by a sliding tackle from former Arsenal midfielder Francis Coquelin.
He was replaced by Pedro Rodríguez, with American summer signing Christian Pulisic overlooked by Lampard.
In the other game in Group H, last season's semifinalist Ajax beat Lille 3-0.
Ter Stegen saves penalty as Barcelona draws 0-0 at Dortmund
Barcelona goalkeeper Marc-André ter Stegen saved a second-half penalty as the Spanish giant began its Champions League campaign by drawing 0-0 at Borussia Dortmund on Tuesday.
Lionel Messi came on as a substitute for the last 30 minutes for his first appearance of the season but was unable to spark the visitors' struggling attack, with Dortmund creating the best chances of the game.
Ter Stegen saved a penalty from Dortmund captain Marco Reus in the 57th and denied the home side with a string of saves on his return to his native Germany.
Dortmund substitute Julian Brandt struck the crossbar and Paco Alcácer also went close against his former side. It was the first game in which the Spanish striker failed to score this season.
The 16-year-old Ansu Fati made his Champions League debut to become Barcelona's youngest player in a UEFA competition, before coming off for Messi in the 59th. Messi hadn't played since injuring his leg in pre-season.
Slavia Prague held Inter Milan 1-1 after conceding a late equalizer in the other Group F game in Italy.
Defender Mats Hummels showed why Dortmund brought him back from Bayern Munich with several vital interventions, starting with a block to deny Antoine Griezmann's first effort for Barcelona, then a crucial headed clearance from the lurking Luis Suárez. Griezmann, on his Champions League debut for Barcelona, produced the cross.
Dortmund's first big chance fell to Reus, who was denied for the first time by ter Stegen in the 25th. Jadon Sancho also missed a good opportunity.
A Barcelona corner caused chaos in the Dortmund defense, with Roman Bürki punching the ball clear and Fati's effort from the rebound deflected over by Reus.
Dortmund was more aggressive after the break but ultimately couldn't get past ter Stegen. Messi, meanwhile, looked far from his best and the home fans cheered loudly when he was crowded off the ball by three defenders as the Argentine failed to make an impact.
Leipzig defeats Benfica 2-1 in Champions League
Timo Werner scored twice in the second half as Leipzig stunned Portuguese champion Benfica 2-1 in Group G of the Champions League on Tuesday.
Werner opened the scoring with a low shot from inside the area in the 69th and doubled the lead from close range in the 78th after a video review reversed an offside call that had initially disallowed the goal.
Substitute Haris Seferovic pulled Benfica closer in the 84th but the hosts were not able to get the equalizer at the Stadium of Light.
In the other group game, Lyon was held by Zenit St. Petersburg to a 1-1 draw at home.
Benfica had lost only one of its last eight European home matches. The Lisbon team was without coach Bruno Lage on the sidelines because of a ban for his sending off in a Europa League game last season.
It was an even match from the start, with the hosts struggling to create significant scoring chances and Leipzig not able to capitalize on its counterattacks until the late Werner goals.
European champions in 1961 and 1962, Benfica has made it out of the Champions League group stage only five times, the last in 2017. It reached the quarterfinals in 2016, losing to Bayern Munich.
This is the second time Leipzig is playing in the group stage of the top European club competition. It made its debut in 2017-18, when it failed to advance to the second round.
Ajax beats Lille 3-0 to open Champions League campaign
Two of Ajax's summer signings scored as last season's semifinalist opened its Champions League campaign by beating Lille 3-0 in Group H on Tuesday.
Netherlands international Quincy Promes opened the scoring in the 18th minute, Mexican midfielder Edson Alvarez doubled the lead five minutes after the break and defender Nicolas Tagliafico added the third in the 62nd as Ajax cruised to victory.
Ajax sold the two biggest stars of last season's run to the semifinals, Frenkie de Jong to Barcelona and Matthijs de Ligt to Juventus, and was missing two more of last season's standouts through injury — attacking midfielder Donny van de Beek and right back Noussair Mazraoui.
But new signings Promes and Alvarez made sure they were not missed at the Johan Crujff Arena.
Promes capitalized on shaky defending to head home a cross by Tagliafico, Alvarez rounded off a long spell of Ajax possession by slamming a powerful shot past Mike Maignan in the Lille goal and Tagliafico headed a corner powerfully into the goal to seal the victory.
Lille at times looked dangerous, with speedy forwards Jonathan Ikone and Victor Osimhen a threat on the break, but both missed good chances and Jonathan Bamba blasted wildly over the bar after another swift counterattack.
Sergino Dest, the 18-year-old United States international who recently extended his contract with Ajax, made his Champions League group stage debut and was rarely troubled on the right side of defense.
Despite coming within minutes of reaching the final last season, Ajax had to win two preliminary rounds to get back into the group stage of Europe's top club competition, beating PAOK Thessaloniki and APOEL Nicosia to earn a berth in Group H alongside Chelsea, Valencia and Lille.
Valencia beat Chelsea 1-0 at Stamford Bridge in the other group game Tuesday.
Amsterdam police detained more than 300 Lille fans for public order offenses at a metro station near the Johan Crujff Stadium before the match started.
Inter draws Slavia Prague 1-1 in Champions League opener
Inter Milan required an injury-time equalizer from Nicolò Barella to earn a 1-1 draw with Slavia Prague in the opening match of the Champions League on Tuesday.
Barella volleyed in the rebound after a free kick from Stefano Sensi hit the crossbar.
Slavia's 23-year-old striker Peter Olayinka was dangerous throughout and put the visitors ahead shortly after the hour mark by turning in a rebound from close range.
Inter won its opening three matches in Serie A to open up a two-point lead atop the Italian league but Antonio Conte's side struggled from the start against the Czech champion, putting only one shot on goal in the first half.
Making matters more difficult, key Inter midfielder Antonio Candreva went off shortly after the break with an apparent injury.
Slavia beat CFR Cluj 1-0 twice in the playoffs to qualify for the group phase, having given eventual champion Chelsea a strong challenge in last season's Europa League quarterfinals, losing on 4-3 aggregate.
Barcelona was visiting Borussia Dortmund later in the other Group F match.
Slavia nearly doubled its lead but a free kick from Nicolae Stanciu went just wide and then an attempt from Lukás Masopust sailed high.
Slavia goalkeeper Ondrej Kolár, who was also a key to the success against Cluj, prevented Inter from scoring a late winner when he made a one-handed save to deny Romelu Lukaku's header in the final minutes of injury time.
Slavia had lost all of its six previous matches in Italy.
Depay's penalty rescues 1-1 draw for Lyon against Zenit
Memphis Depay's second-half penalty salvaged a 1-1 draw for Lyon at home against Zenit St. Petersburg in the Champions League on Tuesday.
Zenit took the lead through a goal from Serdar Azmoun in the 41st minute before Depay was tripped on the edge of the area by Magomed Ozdoev, who had just come on as a replacement for the injured Azmoun. The Dutch winger blasted his 50th-minute penalty into the bottom-left of the goal, leaving goalkeeper Andrei Lunyov no chance.
It was a frustrating night for Lyon, which had gone close with a header by Marcelo in the first half, and could have won the game in the second if Jeff Reine-Adelaide's shot hadn't gone narrowly wide.
Azmoun became the first player to score in this season's Champions League, shooting low in the 41st after a one-two with Artyom Dzyuba. He had suffered an apparent ankle injury just before the goal and was substituted early in the second half.
He was also the first to have his goal checked by the video assistant referee system, which helped referee Michael Oliver dismiss Lyon's protests of offside. The VAR system was only used in the knockout rounds last season and was making its debut in the group stage Tuesday.
Group G is widely considered the most open of this year's Champions League, and also includes Benfica and Leipzig.