It took a mere three minutes for Barca to break the deadlock, and it came courtesy of a superb first-time finish from Ferran Torres, who timed his run perfectly to meet Alejandro Balde's precise through ball before firing past Stole Dimitrievski.
Torres struck again 15 minutes later to leave Los Che already staring down the barrel of elimination, as the former Manchester City, and Valencia, man fired home on the rebound after Lamine Yamal’s initial effort cannoned off the post.
Valencia thought they may have earned a reprieve when the strike was initially ruled out for offside, but VAR intervened and allowed the goal to stand.
The Mestalla crowd grew even more restless when Fermin Lopez added a third, brilliantly taking Pedri’s pass into his stride before prodding the ball past Dimitrievski.
Torres then completed a stunning first-half hat-trick on the half-hour mark when he clinically dispatched a right-footed strike into the bottom corner from Raphinha’s brilliant lay-off, adding to a chastening first half for the hosts.
It was the fastest hat-trick for Barcelona in any competition since Samuel Eto'o scored three inside 28 minutes against Almería in LaLiga in October 2008.
Umar Sadiq thought he had given the long-suffering Mestalla crowd something to cheer when he converted an angled finish past Wojciech Szczesny, but it was chalked off for offside.
Down the other end, Yamal came inches away from adding a fifth Barcelona goal, only to see his strike clip off the post.
The teenage starlet would soon add his name to the scoresheet though, as his shot squirmed past Dimitrievski with Raphinha registering another assist.
This goal-fest on the road means Hansi Flick’s side have now failed to score in only one of their 20 away games this season, with nine of those matches resulting in more than four goals for the Catalans.
Meanwhile, Carlos Corberan’s team will be sick of the sight of Barcelona, having conceded 14 goals in their three meetings this season, and will now focus on preserving their LaLiga status.