Few teams have caused as much trouble for Barcelona as Chelsea since Lionel Messi started playing with the Spanish club almost 15 years ago.

Barcelona has been dominant with Messi against nearly every opponent it has faced in Europe.

But not against Chelsea.

The English club is even used to doing well against Barcelona at Camp Nou Stadium, where the teams will meet Wednesday in the second leg of their last-16 series in the Champions League.

Chelsea is unbeaten against Barcelona in eight matches, with four straight draws at Camp Nou.

Chelsea's Pedro Rodriguez kicks the ball during a training session at the Camp Nou stadium in Barcelona, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg Wednesday. (AP Photo/Manu Fernandez)

Barcelona earned a 1-1 draw in the first match in England thanks to a late away goal by Messi, who had never scored against the Premier League club.

"It will be a hard match just like in the away leg," Barcelona coach Ernesto Valverde said. "They have a strong team that defends well in a block and has a great counterattack. We will struggle."

Barcelona has been thriving again this season. Its only loss came against Real Madrid in its first match of the season in the Spanish Super Cup final. It has won 18 of its last 20 home matches since then, with two draws — 2-2 against Celta Vigo and 0-0 against Getafe in the Spanish league.

"We have to show great resilience," Chelsea coach Antonio Conte said. "We are playing against one of the best teams in the world. We must pay great attention and have the same focus and concentration of the first leg."

Chelsea's Marco Alonso, right, kicks the ball during a training session at the Camp Nou stadium in Barcelona, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg Wednesday. (AP Photo/Manu Fernandez)

This is the first time Chelsea and Barcelona are facing each other in the Champions League since the semifinals in 2012, when the English club advanced 3-2 on aggregate after securing an astonishing 2-2 draw in the second leg at Camp Nou, after trailing 2-0 with 10 men for most of the match.

Chelsea also drew at Camp Nou in the Champions League semifinals in 2009, as well as in the group stage of the 2006-07 season and the round of 16 a year earlier.

Chelsea is trying to make the quarterfinals for the first time since 2014, when eliminated by Atletico Madrid in the semis. Barcelona is looking to reach the last eight for a record 11th straight time.

The Spanish league leaders are coming off a 2-0 win at last-place Malaga on Saturday, when Messi didn't play because of the birth of his third son, Ciro.

It remains unclear if Valverde will be able to count on midfielder Andres Iniesta on Wednesday because of a hamstring injury.

Chelsea's player Cesc Fabregas, front, attensd a training session with his teammates at the Camp Nou stadium in Barcelona, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg Wednesday. (AP Photo/Manu Fernandez)

Conte says he expects Chelsea to 'suffer' against Barcelona

Antonio Conte doesn't hide it: He expects Chelsea to struggle against Barcelona at the Camp Nou.

The teams meet Wednesday in the second leg of their round-of-16 matchup in the Champions League, with Barcelona carrying a slight edge after earning a 1-1 draw in the first match in London. Chelsea needs to score at least a goal to be able to advance.

"There may be times that we suffer, but we have to stay compact and when you have the ball you must have the belief in your head and heart that you can score," Conte said Tuesday. "We have to stay in the game, but it won't be easy. If we want to go through to the next round we must invest in the game for every moment of it."

Chelsea had a good performance in the first leg, containing Barcelona until conceding a 75th-minute equalizer after a mistake by 21-year-old defender Andreas Christensen. He made a poor pass across the penalty area and Andres Iniesta intercepted the ball before feeding it to Lionel Messi, who scored from inside the area for his first ever goal against the English club.

FC Barcelona's coach Ernesto Valverde attends a press conference at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen, second leg on Wednesday. (AP Photo/Manu Fernandez)

"In the first leg we played a really good game — almost a perfect game — against a team I consider one of the best in the world," Conte said. "The final result for the first leg gives a great advantage to Barcelona. We know their philosophy will be to win the game and we have to try to do our best, have great concentration and keep our heads on the pitch the whole time."

Despite Conte's praise for Barcelona, Chelsea has done well against the Spanish powerhouse recently, including at Camp Nou.

The English club is unbeaten against Barcelona in eight matches, with four straight draws at the opponent's stadium. The most significant one came in the 2012 semifinal, when Chelsea came back from two goals down with 10 men to earn a 3-2 aggregate win that kept it on track to securing its lone Champions League title.

Barcelona, a five-time European champion, eliminated Chelsea in the 2009 semifinals, when Iniesta scored the decisive goal in second-half injury time in the second leg in London.

FC Barcelona's Andres Iniesta, second right, attends a training with his teammates at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg football match on Wednesday. (AP Photo/Manu Fernandez)

Iniesta's return key for Barcelona against Chelsea

Andres Iniesta has a knack for great performances against Chelsea.

His injury-time goal in the semifinals of the 2009 Champions League remains one of the most important of his career. And he also scored against the English club in the 2012 semifinals, even though Barcelona was eliminated that time.

In the first leg of this year's encounter between the two teams, it was Iniesta who set up Lionel Messi's important away goal in a 1-1 result that gave the Spanish club an edge going into Wednesday's return match at Camp Nou Stadium.

It's unclear, though, if Iniesta will get a chance to thrive against Chelsea again on Wednesday. The midfielder is nursing a hamstring injury in his right leg and is listed as doubtful for the second leg.

FC Barcelona's Andres Iniesta, second right, attends a training session with his teammates at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg on Wednesday. (AP Photo/Manu Fernandez)

The 33-year-old Iniesta had to be replaced in the first half of Barcelona's Spanish league match against Atletico Madrid on March 4. He grabbed his right thigh before going down and requesting medical attention in the 22nd minute at Camp Nou. He returned to the match but lasted only about 10 minutes before being substituted.

Iniesta was expected to be out for at least two weeks but appeared to be recovering ahead of schedule. He practiced with the rest of his teammates Monday for the first time since the injury, finishing the session without any problems. He also was on the pitch during the team's final practice on Tuesday.

"It's a huge game, and you need to be 100 percent ready to play in games like these," Barcelona coach Ernesto Valverde said Tuesday. "We will see how he does in the last training session and then we will make a decision.

"Of course, when it comes to an elimination match, the player is more inclined to take risks," Valverde said. "But you have to weigh how big is this risk."

From left, FC Barcelona's Andre Gomes, Samuel Umtiti, Gerard Pique and Lionel Messi attend a training session at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg football match on Wednesday. (AP Photo/Manu Fernandez)

Chelsea coach Antonio Conte said it would be good for football if Iniesta got to play.

"We are talking about a great player. There are many great players, with great talent, but he is a football genius," Conte said. "I don't know if he will play, but in games like these it is right that you face the best players, so I hope he doesn't miss out."

Iniesta's importance for Barcelona goes beyond his past heroics against Chelsea.

The team's captain, Iniesta has been crucial for the Catalan club recently as the team's other midfielders have struggled.

"We all know what Andres adds to the team, both on the field and as the captain," Barcelona midfielder Sergio Busquets said. "You give him the ball and he always knows what to do with it. He always brings something positive. We have one last training and we hope that he will be fit. He will have the last word."

FC Barcelona's Lionel Messi takes part during a training session at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Spain, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second leg Wednesday. (AP Photo/Manu Fernandez)

If Iniesta can't play Wednesday, Valverde won't have an easy time picking his substitute.

Andre Gomes, who replaced Iniesta when he had to leave the match against Atletico, has been constantly jeered by part of Barcelona fans because of his lackluster performances. Paulinho started the season well but hasn't played at the same level recently, and Denis Suarez is out injured.

Philippe Coutinho could have been a viable option but he is ineligible after having already played in this season's Champions League with Liverpool before being signed by Barcelona.

"We don't have anyone similar, because Iniesta is unique, but there are players who can play in a similar function, like Denis, Coutinho, Gomes ...," Valverde said. "We have several options, we'll see."

Valverde could even consider drastically changing the team's tactical scheme by replacing Iniesta with Ousmane Dembele, who played well in the team's 2-0 win at Malaga in the Spanish league on Saturday. It would be a much more aggressive set up, adding another forward to play alongside Messi and Luis Suarez.

FC Barcelona's Sergio Busquets attends a press conference at the Sports Center FC Barcelona Joan Gamper in Sant Joan Despi, Tuesday, March 13, 2018. FC Barcelona will play against Chelsea in a Champions League round of sixteen second next Wednesday. (AP Photo/Manu Fernandez)

Messi, who is having another stellar season, is certain to return to the squad after missing the Malaga match because of the birth of his third son, Ciro.

Messi scored the equalizer in the first leg after Iniesta smartly recovered a ball in attack and avoided a defender's tackle before making a soft pass to the Argentina playmaker inside the area.

In 2009, it was Messi who rolled the ball for Iniesta's strike from outside the area in the third minute of injury time at Stamford Bridge, silencing the Chelsea crowd and putting Barcelona on track to winning another Champions League title.

Iniesta was optimistic he would get another chance to thrive like that against the English club.

"Getting closer," he said, "day after day."