Barcelona were ahead within five minutes when Lamine Yamal hooked the ball over Stole Dimitrievski from Fermin Lopez's floated ball in behind.
The 19-year-old thought he'd doubled the lead three minutes later, but VAR overruled the effort for offside.
Barca's 80% possession meant it was just after the quarter-hour before Valencia even got close to the visitors' goal, with David Otorbi wasting the opportunity.
Almost immediately, Barcelona went up the other end and Fermin arrowed a left-footed shot into the bottom corner.
Arnaut Danjuma had Barca keeper Joan Garcia scrambling after Rodri's error midway through the half, though it was Barca who went closest to scoring before half-time when Fermin's quick feet saw him create the space for a shot that came back off the woodwork.
Nothing changed after the break, and the visitors had already seen a decent chance go begging before Raphinha tapped in a third from almost on the goal line.
A bullet header from Rodri saw the crossbar rattled, and the 'training ground' feel to the match continued.
Multiple substitutes from the hosts couldn't change the pattern of the game, and with just over 10 minutes to play, Pedri's give-and-go with Dani Olmo ended with the former tucking home a fourth.
Yamal then rubbed salt into the wounds with a fifth shortly after, with Olmo again the provider.
The defeat means Valencia have now equalled their worst four-game start to a new season in the past 10 years, whilst Barcelona continue their dominance over Los Che, with an 11th win in the last 14 H2Hs.
Flashscore Man of the Match: Fermin Lopez (Barcelona)
