And PSG also outplayed United in the first leg of their last-16 clash - before being blown away in the return fixture at the Parc des Princes.
The statistics from this season suggest his chief priority in the transfer market this summer should be rebuilding a defensive line that have conceded 60 goals in the 46 games they have played this season in all competitions.
"We had five uncomfortable minutes because they came out strong".
Four minutes later, the United goalkeeper endured a calamitous moment, allowing Messi's tame right-footed shot to squeeze beneath his body and into the net.
With so many stars under performing United need a player to step up and get the season back on track.
Lionel Messi scored a first-half brace as Barca accounted for United 3-0 at Camp Nou on Tuesday, sealing a comprehensive 4-0 aggregate victory.
"The image (we gave) was spectacular".
"Messi is fine", said Barca coach Ernesto Valverde.
United started the game in excellent fashion as Marcus Rashford clipped the top of the bar after little more than 30 seconds. The important thing is that we achieved our goal. If you sign up to a service by clicking one of the links, we may earn a referral fee.
The Norwegian has a huge task to do and his side are still in contention for a top four finish, though you wonder whether United would be better not being in the Champions League next season because they are well short of the quality required to win it.
At the final whistle, when Smalling approached to shake his hands, Messi ignored the gesture instead responding with a brief tap on his back, before moving onto embrace other players.
Even going behind to a goal from Ronaldo in the first half didn't faze Ajax's young players as Donny van de Beek leveled shortly after and 19-year-old captain Matthijs de Ligt scored the victor in the second half.
The last time Manchester United exited the Uefa Champions League at the quarter final stage in April 2014, they travelled to Everton on the following Sunday.
We started well in the first 15 minutes, we felt "we've got something here" and then in four minutes they scored two goals.
"Cristiano increased our chances of winning the Champions League but football isn't math", Allegri added.
"And of course one or two additions to the squad will happen in the summer".