Kylian Mbappe and Paris Saint-Germain handed Manchester United a reality check under Ole Gunnar Solskjaer, winning 2-0 in the Champions League last-16 Tuesday to inflict the interim manager's first loss.
Angel Di Maria was the architect of both goals in the first leg on his return to Old Trafford as PSG more than coped without injured forwards Neymar and Edinson Cavani.
The winger's corner was volleyed in by Presnel Kimpembe for his first PSG goal in the 53rd minute. After having a bottle thrown at him by United fans and taking a sip, Di Maria helped to complete a counterattack by crossing for the advancing Mbappe to score.
United will be without Paul Pogba in the second leg on March 6 in Paris after he received a second yellow card in the 89th minute for a lunge on Dani Alves.
"I know Paul wants to just shield the ball so he's unlucky that he hits (Alves) on the knee," Solskjaer said.
Without two of its usual front three, the French league leader commanded the midfield instead, with Marco Verratti the orchestrator.
"It was a new system and we weren't really used to it," Mbappe said after scoring his 23rd goal of the season. "We had a lot of midfielders and not many forwards. We needed time to adapt, even though you can get punished for that in the Champions League."
But it was United that was exposed instead.
Not only was it a first loss for Solskjaer in his 12th match since replacing Jose Mourinho, but the heaviest-ever home defeat for United in Europe, having previously only been beaten by one-goal margins.
In the night's other last-16 game, teenager Nicolo Zaniolo scored twice to lead Roma to a 2-1 victory.
United's lackluster performance was a continuation of the European form under Mourinho in the group stage. United has only scored one goal at home in four Champions League games this season, a 1-0 victory over Young Boys.
"It was one of those experiences that can go either way," Solskjaer said. "It's not going to be a season-defining one for us. It has to be one that we are going to learn from."
Aside from victories in north London against Arsenal and Tottenham, facing PSG was United's biggest test since beating Italian champion Juventus in Turin in November in the group stage.
"You can see we haven't played games at this level for a while," Solskjaer said.
Twenty years after winning the Champions League as a United player, this was Solskjaer's first taste of the competition in management having only previously coached Molde in his native Norway and Cardiff before being hired by United.
Teenager Zaniolo scores 2 as Roma beats Porto 2-1
Teenage midfielder Nicolo Zaniolo proved he can shine on the European stage, scoring both goals to give Roma a 2-1 win at home against Porto in the first leg of the Champions League round of 16 on Tuesday.
Zaniolo has emerged as one of Serie A's most promising talents this season since his transfer from Inter Milan in the offseason as part of the deal which saw Radja Nainggolan move the other way.
And the 19-year-old added his first Champions League goals by netting the 70th and 76th minute for Roma, before Adrian Lopez pulled one back for Porto three minutes later to give the visitors hope ahead of the return leg on March 6.
"It's a memorable night that I will never forget in my life," Zaniolo said. "Celebrating under the Curva Sud was an incredible emotion, I hope I will score many more important goals for Roma.
"The late goal we conceded can be tricky for us ahead of the return leg but we will just continue working hard to try finishing the job in Portugal."
Zaniolo, who turns 20 in July, is the youngest ever Italian player to score two goals in a match in Europe's premier club competition.
"Zaniolo will become a real champion, not just according to me but according to everyone," Roma captain Daniele De Rossi said. "His physical strength is incredible for a guy of his age and he combines it with great technique."
The opening goal came after Edin Dzeko knocked down Stephan El Shaarawy's cross for Zaniolo to drill past Iker Casillas and into the far bottom corner. The teenager doubled his tally by tapping in the rebound after Dzeko's shot came off the left post.
It was the second time Dzeko had hit the post.
Porto, which was undefeated in the Champions League this season, got a valuable away goal with a bit of luck when Tiqinho Soares's effort was so poor that it bounced into the air and turned into an assist for Lopez, who fired into the far corner.
"In our own stadium, in front of our own fans, we've still got what it takes to go through," Pepe said.
Video review was being used for the first time in the Champions League and it was called into play in the 18th minute but a check ruled that Pepe's handball in the penalty area was unintentional.
In the night's other Champions League match, Ole Solskjaer suffered his first defeat as Manchester United coach as his side lost 2-0 at home to Paris Saint-Germain.
Presnel Kimpembe and Kylian Mbappe scored for PSG in the second half, while Paul Pogba was sent off late on following two yellow cards.