The semi-final against Barcelona is finely balanced after a 0-0 draw in the first leg at the Nou Camp, with Cristiano Ronaldo's penalty miss after three minutes depriving United of a precious away goal.
Barcelona soon recovered from that scare and had the majority of possession but failed to hurt United.
Asked if his side would be more aggressive in the return match, United boss Ferguson said: "Absolutely, no question about that.
"The game now starts at Old Trafford - it's the deciding game.
"A scoring draw and we're out, a loss and we're out, but the big bonus is that if we win we are through to the final.
"At Old Trafford, with the atmosphere, it will be quite different to this game.
"Barcelona have a lot of possession in all games, especially at home, and I am satisfied with the clean sheet - it was a professional performance."