Despite the goals and other chances at either end, the first half’s big talking point was the decision by the ref to only book Fred instead of showing a red card, after reviewing on the pitch-side monitor an apparent movement of his head into Leandro Paredes’ face.
After the break Anthony Martial missed a great chance and Edinson Cavani hit the bar with a brilliant chip, before Fred was finally dismissed and Marquinhos put PSG back in front, with Neymar wrapping up the win late on.
Here are five things we learned from the match at Old Trafford.
Fred the red
PSG will think United’s midfielder could easily have had two red cards, never mind just one.
He first clattered through the back of his man - no card - then clearly moved his head in the face of Paredes, a red card for pretty much every referee every day of the week, only for a yellow to be shown after a video review, which is a rarity in itself.
Then there was yet another foul from the Brazilian which went unpunished and yet Ole Gunnar Solskjaer opted to leave him on the pitch - and the red card duly arrive a little after the hour mark.
Of course, in keeping with the other poor decisions from the ref, the tackle Fred actually received the sending-off for was the challenge he actually won the ball in: good timing, poor judgement to do it anyway.
Neymar, good and bad
Always a two-sided coin with the No. 10.
He started the game in the mood and in the groove, scoring a fantastic finish and creating danger almost every time he got on the ball. Later, he teed up Mitchel Bakker for a great chance, his set pieces were good and he was the usual outlet for his team to relieve pressure.
But, in between, he had to get himself involved in the other side of his game, the narky and the confrontational, the complaints and the downright nasty.
Several times he clashed with Scott McTominay, mostly being fouled and once even being stood on, so an amount of frustration is understandable. But he also put himself in the middle of the arguments he had no part of, left a foot in late more than once and made one or two kicks out of the type he doesn’t hesitate to draw attention to when they come his way.
Obviously, he had to have the last word with another goal, a tap-in after a brilliant dribble and pass to start the move, too.
Fred aside, there were a couple of disappointing performers in red for the home team.
Alex Telles was largely poor with his delivery, failed to deal decisively with crosses and runs in behind his side of the defence and generally underperformed on a big night.
Anthony Martial was both almost good and ultimately poor, missing an absolutely huge chance from close range and seeing another powerful drive blocked, but also creating a few openings for his team - so perhaps this was a step forward from recent games, rather than just a poor night.
But the biggest disappointment was probably Bruno Fernandes, a real bystander for most of the game considering his usual level of impact for the team.
After the success of United’s recent games against PSG it was a real surprise to see Solskjaer not going with the back three - or five, realistically - which had so frustrated the French side.
A 4-2-3-1 was bold, but too open, lacking the bodies in defence which thwarted the Ligue 1 outfit in Paris and previously.
Perhaps this was an attempt to take advantage of good recent form, but it backfired if so - PSG were always a big danger on the break despite United’s own chances on goal.
United remain on the brink
This is the group of drama, not group of death. PSG’s win, plus Leipzig’s injury-time win over Basaksehir, means the top three are locked on nine points.
A point for United is enough, while PSG also need the same outcome from their last game to be assured of a last-16 spot. Leipzig have to win, unless Basaksehir can beat PSG - and the Turkish side now have nothing to play for.
At the start of the group phase United fans might have taken this position, needing to avoid defeat on the final night to progress, but it will surely be a case right now of looking back at the defeat in Istanbul and wondering if a dreadful night will prove costly.
It all hinges on the next week.