Goals from Luis Suarez and Samuel Umtiti earned the league leaders a slice of history and helped to banish thoughts of Wednesday's Champions League capitulation against Roma, despite Dani Parejo's penalty.
A rainy day and a subdued crowd of just 69,544 spectators – well short of the 99,354 capacity – was reflected in a turgid opening spell for Barca, until Suarez struck to break the deadlock and restore some cheer to the stands 15 minutes in.
Valencia had chances to level the scores, with Goncalo Guedes and Rodrigo Moreno wasting clear opportunities, before the under-fire Umtiti responded to his critics by heading in the second goal after 51 minutes.
Marcelino's Champions League hopefuls got a goal back through Parejo's late penalty but could not complete the turnaround, ensuring Barca surpassed the previous record of 38 games unbeaten that they shared with Real Sociedad in winning fashion.
The result also moves the leaders 14 points clear at the top of the table, with second-place Atletico Madrid playing their game in hand against Levante on Sunday.
Guedes forced Marc-Andre ter Stegen to claw away a fine strike during a sluggish opening spell from Barca, but Suarez soon had the fans on their feet.
Philippe Coutinho, restored to the side after being cup-tied for the Roma loss, threaded a fine throughball into Suarez's path and the striker side-footed past Neto at the right-hand post.
lencia responded well, though, Guedes seeing a low striker saved by Ter Stegen before firing a deflected effort just wide after picking up a loose ball in the Barca box.
Ter Stegen gifted the visitors another chance with a poor clearance but made amends in style, turning Rodrigo's effort onto the crossbar with an excellent one-handed save.
Rodrigo should have punished an Umtiti error early in the second half but his effort was cleared off the line by Gerard Pique after Santi Mina had played him into clear space in the penalty area.
The miss proved costly. A minute later, Coutinho's corner was headed into the bottom-right corner by Umtiti, despite Neto's best efforts to keep the ball out.
Dani Parejo came close with a 35-yard free-kick but captain Andres Iniesta could have made it 3-0, with Neto reacting well to parry his volley from Lionel Messi's cross.
Messi himself shot just wide at the end of a mazy run before Parejo squeezed an 87th-minute penalty beneath Ter Stegen, after Ousmane Dembele carelessly brought down Jose Gaya, but it made little difference to Barca's record-breaking day.
