The good news for Barcelona was that Gerard Piqué, 34, was back in the back line again after a knee injury he suffered in November.
PSG, on the other hand, had to do without Neymar.
The 29-year-old was replaced injured against Caen in the French Cup, on February 10, and thus misses the round of 16 in the Champions League against Barcelona.
Barcelona took the lead
Messi started the goal scorer in the match.
With 29 minutes played, the visitors broke through on the right after some poor defending.
However, 22-year-old Frenchman Kylian Mhappé would, three minutes later, sign for his PSG.
That when he got past Piqué and coolly put 1-1.
Hattrick by Mhappé
Mhappé would score both 2-1 and 4-1 in the second half.
By then he had completed his hat trick.
- It is a great quality of what Mhappé has done out there today - in addition to the three goals, says Viasat expert Glenn Strömberg.
The text is updated.