Messi powers Barcelona victory
Messi started his treble in the 11th when Sergio Busquets intercepted a pass and shuffled the ball to Cesc Fabregas, who then used one touch to send Messi charging into the area and over goalkeeper Diego Alves before rolling the ball home.
The sequence of Busquets robbing the ball, Fabregas assisting, and Messi scoring repeated itself in the 39th.
Barcelona coach Gerardo Martino had said after Barcelona's 0-0 draw against Atletico Madrid earlier this week that he wanted Messi and Neymar to link up more in attack.
Martino got what he had asked for when Neymar picked out Messi arriving down the middle of the area to slice his pass into the net for his league-leading fifth goal in two games after sitting out one match due to a muscle problem.
But just when it appeared Barcelona would romp, Valencia striker Helder Postiga used an acrobatic volley to pull one back in the 44th before he scored with a header from a corner kick in first-half injury time.
Neymar was involved twice more in almost getting Messi another goal, only to see the Argentine miss both late chances before Valencia substitute Jonas hit the post four minutes from time.
''The concern that Messi and Neymar didn't combine in their first game together, well, they solved that in 24 hours,'' Martino said.
Barcelona said Busquets ended the match with pain in his right leg and will undergo tests.
Sociedad's Xabi Prieto halved the final difference in the 69th in a clash between two teams set to make long-awaited returns to the Champions League.
Atletico, Barcelona, Madrid and Villarreal are the only teams with three wins in as many rounds.