After barca's shock midweek home defeat to Granada saw Barca squander the chance to go top of La Liga, Ronald Koeman's side were in desperate need of a victory when they headed to Valencia, even more so given title rivals Atletico Madrid and Real Madrid both won on Saturday.
Things weren't going to plan when Gabriel Paulista headed the hosts in front just after the restart.
But Messi levelled matters in the 56th minute, slotting home after his initial penalty had been saved.
Antoine Griezmann then turned the game on its head five minutes later when he poked in a loose ball and Messi put the visitors in the ascendency with a stunning free-kick soon after.
The little wizard fired his set-piece past the diving Jasper Cillessen and in off the post. Pure poetry from the Argentine ace.
