Quique Setien suffered his first defeat as Barcelona manager as Valencia claimed their first home win over the Spanish champions since 2007.
Setien had enjoyed a good start to his Barca reign, guiding the club to victories over Granada in La Liga and UD Ibiza in the Copa del Rey round of 32.
The visitors were quick to gain a stranglehold on possession but were almost non-existent as an attacking force in the first half, with Valencia enjoying the better of the early chances.
Valencia came into Saturday’s clash having beaten Barca in just one of their past 10 meetings in all competitions, winning last season’s Copa del Rey final, while their most recent league success at the Mestalla came in February 2007.
The hosts broke the deadlock when Jordi Alba deflected Maxi Gomez’s powerful strike past Marc-Andre ter Stegen.
Gomez, who had a first-half penalty saved by Ter Stegen, completed the scoring in the second half as he ended the visitors’ hopes of a late revival with 13 minutes remaining, curling into the far corner after Ferran Torres had broken clear down the right wing.
Barcelona started the second half with greater purpose and Ansu Fati almost fashioned an opening after combining well with Lionel Messi, but the teenager could only poke his shot straight at Jaume Domenech in the Valencia goal.
Messi appeared eager to take matters into his own hands as the second half progressed, dragging a fierce low effort wide of the far post before heading off target from a good position.
Former Arsenal defender Gabriel Paulista thought he had made it 3-0 late on, but the Brazilian’s volley was disallowed for an infringement inside the Barcelona box.
Second-placed Real Madrid can move three points clear of Barcelona at the top of La Liga if they win their game in hand at Real Valladolid later today.
There were unsavoury scenes before the game as rival fans clashed outside the Mestalla Stadium.