Los Che actually took the lead in Catalunya, with Pablo Piatti striking just nine minutes in, but they were then blown away by Lionel Messi, who netted four times before Xavi put the seal on a comprehensive victory for the hosts by netting shortly after coming on as a substitute.
Emery admitted afterwards that his side had been utterly outclassed for the most part, but argued that his troops had been unusually below par.
"We had a bad game," the Valencia boss is quoted as saying by AS. "It's a painful defeat because we have been so inferior.
"On other days we have played good games; today was quite the opposite.
"It's not whether it was humiliating or not; it's just that they were far superior. We were at their mercy.
"We saw the best version of Barcelona and one of the worst versions of Valencia. Clearly we were poles apart."
Emery admitted that his side's dismal showing at Camp Nou had topped off a desperately disappointing day for Valencia, who had earlier announced that midfielder Ever Banega is likely to be out of action for six months with a broken ankle after accidentally running over himself with his own car.
"It's unfortunate news in every way," Emery said. "Obviously we are concerned and most importantly we hope he gets well soon. But now we must look for alternatives."
Valencia remain third in La Liga but are now 11 points adrift of second-placed Barca.
Since November, Goal.com has been publishing exclusive extracts from Graham Hunter's highly-anticipated new book, 'Barca: The Making of the Greatest Team in the World'. The very last extract, which was published on Friday, looks at Andres Iniesta's risky return from injury in the 2009 Champions League Final and how he was described by Wayne Rooney as the 'best midfielder in the world'. Don't miss it!