Sixteen-year-old Ansu Fati was the star of the show on his full debut, registering a goal and assist inside the opening seven minutes and posing a constant threat throughout his hour on the field.
Kevin Gameiro did pull one goal back after Frenkie de Jong had doubled Barca's early advantage, but Gerard Pique restored that two-goal cushion six minutes into the second half before Luis Suarez - who replaced Fati off the bench - helped himself to two goals in the final half an hour.
There was a late consolation for Valencia through Maxi Gomez on their first outing since surprisingly sacking Marcelino and replacing him with Albert Celades, but Barcelona's win was never in doubt as they made it back-to-back 5-2 triumphs at home in the league, having taken just one point from their two away games so far.
The latter immediately repaid that faith by opening the scoring inside two minutes, adding to his goal from the bench against Osasuna last time out with his first strike at Camp Nou - becoming the youngest-ever Barcelona player to score on home soil in the process.
De Jong created the goal with a low pass into the box which was cleverly left by Antoine Griezmann for Fati, who met it with a firm first-time finish which left former Barca keeper Jasper Cillessen no chance in the Valencia goal.
While it was a dream start to the youngster's full debut for the club, it was a nightmare for former Barca midfielder Celades, who fell behind less than two minutes into his first match in charge of the visitors.
Matters only got worse moments later when the roles were reversed for Barcelona's second, this time Fati providing the assist and De Jong blasting it home.
Ezequiel Garay could not live with the pace and footwork of the teenager, who skipped down the left channel before pulling the ball back for De Jong to also open his Camp Nou account with a powerful first-time finish.
For all the money spent on Griezmann this summer - not to mention the star power missing from Barcelona's lineup - it was Fati who continually looked the most dangerous for the home side and he came close again after 16 minutes when his deflected shot flashed inches wide of the target.
Valencia saw just 18% of the ball in the opening 15 minutes as Barcelona dominated, but the visitors did begin to grow into the game a little more as the half wore on and Gameiro had their first sight of goal when he was released by Rodrigo Moreno only to slice his finish wide of the near post.
It proved to be a warning that the hosts did not heed as Gameiro halved the deficit shortly afterwards, latching on to another Rodrigo pass before this time sliding his finish past Marc-Andre ter Stegen and in off the inside of the post.
The goal was initially ruled out when the offside flag was raised, but VAR checks showed that Gameiro was indeed onside and the Frenchman's strike was allowed to stand.
Fati almost restored the two-goal lead shortly after the half-hour mark when he again cut inside before firing an effort narrowly wide of the top corner, with Cillessen once more left helpless and relieved to see it fly off target.
The fragility of Barcelona's defence meant that Valencia were always in the game, though, and it took a pair of fine point-blank saves from Ter Stegen to deny Gameiro twice in quick succession - first when one on one at the end of a counter-attack and then from an acrobatic effort after the hosts had failed to clear their lines.
Griezmann had been comparatively quiet next to Fati and blazed a rare first-half sight of goal over the crossbar, but he did have a major role to play in Barcelona's third six minutes after the restart.
The Frenchman's low shot from the edge of the area squirmed underneath the body of Cillessen before bouncing against the inside of the post, and Pique was the unlikely figure to react quickest to the mistake, showing a distinct striker's instinct to tap home the loose ball from close range.
Three almost became four moments later when Nelson Semedo drilled a low strike towards goal which again had Cillessen beaten, although this time the woodwork came to the goalkeeper's aid as the ball bounced to safety off the inside of the post.
Fati's memorable home debut came to end on the hour mark when he was replaced by Suarez to a standing ovation, and the Camp Nou crowd were soon back on their feet to salute the returning replacement as he made an immediate impact.
Just a minute after his introduction the Uruguayan secured all three points for the hosts, making it 4-1 with a pinpoint curling finish which beat Cillessen at the near post before going in off the inside of the upright.
It took a triple save from Cillessen to prevent things from getting even worse for Valencia shortly afterwards, with the former Barca shot-stopper thwarting Griezmann when one on one before denying follow-up efforts from Perez and Arthur.
Suarez was the next to force a save from Cillessen and Sergio Busquets also threatened a fifth with a curling strike from range which ended up a couple of yards past the post.
Valverde's side did add a fifth with eight minutes of normal time remaining as Suarez doubled his tally during a productive cameo, applying a very similar finish to his first goal by beating Cillessen with a curling snap shot at the near post.
It was a harsh lesson for Celades, who spent time at both Barcelona and Real Madrid during his playing career and more recently was assistant at the latter, but there was a late consolation for him to cheer as Gomez finished from close range with the last meaningful action of the match.
The result lifts Barcelona up to fourth in the table ahead of their Champions League opener at Borussia Dortmund on Tuesday, while Valencia will look to bounce back from this defeat against Chelsea at Stamford Bridge.
BARCELONA (4-3-3): Ter Stegen; Semedo, Pique, Lenglet, Alba; De Jong (Rakitic 70'), Busquets, Arthur (Vidal 73'); Perez, Griezmann, Fati (Suarez 60')
VALENCIA (4-4-2): Cillessen; Wass, Garay, Gabriel, Gaya; Torres (Lee 67'), Coquelin, Parejo, Guedes (Cheryshev 67'); Gameiro, Rodrigo (Gomez 72')body check tags ::