Shaun Wright-Phillips, Nicolas Anelka, Kevin Horlock and Chris Shuker were on target for Kevin Keegan's men.
"The Rochdale game was a good work-out for the lads, but with all due respect, I think we now need to step it up and the Barcelona game will give us the chance to do that," said the City boss after the game.
"By that stage, we should have Paulo Wanchope and Darren Huckerby fit after injuries, so the signs are looking good. The two of them may even be fit to take part in a probables v possibles game we are having on Wednesday."
Click here to see Wright-Phillips' goal