Ferdinand admitted the team had been punished for being careless.
Ferdinand told MUTV: "We gave them the impetus to claw their way back into the game. We played some great football at times but were so careless at times. If you are careless you are going to get punished. That was the case.
"There wasn't a mental reaction to Tuesday but maybe physically you could see it in a few of the guys' legs, and as the game stretched and became a bit more open there were some tired legs out there.
"But that is no excuse. We should have had the game sewn up before then and with the experience out on the pitch we didn't utilise it the way we should have.
"But we are still in the cup. Wembley is waiting for one of us to go through and hopefully it is us.
"We go to Stamford Bridge for the replay with confidence. We have the tools. We have been there before this season and done well, and with the squad we have we don't fear going anywhere."