The Reds got off the mark in the third minute from the penalty spot after Aaron Hughes' handball. And United should arguably have had a second soon after when Damien Duff clearly handled in the area.
"I think from the referee's position he obviously thought it was unintentional, but from my angle - obviously I've got the benefit of looking at the video at half-time - it was handball," added Sir Alex. "But we didn't need any decisions because the performance was good.
"We had some shots in the first half blocked, one hit the bar - we needed that second goal to put us in the comfort zone, and we got that early in the second half and then a third and fourth followed."
"We picked a very strong team because we didn't want to make any slip-ups. The FA Cup is an important trophy for us this season. We haven't won it for nearly 10 years."
- Sir Alex Ferguson