Sir Alex Ferguson apologised to fans after Manchester United were held to an embarrassing goalless draw by non-league Exeter.
The Old Trafford faithful booed their side off the pitch and Ferguson said: "I apologise, they didn't deserve that.
"In my 18 years at this club, that was the worst performance we have ever produced in the FA Cup.
"This is Exeter's day and the only positive thing we can take is that we're still in the competition."
Although Ferguson took the opportunity to rest key players, he was not prepared to offer that as an excuse as they head to St James Park for an unwanted and unexpected replay.
An angry Ferguson said: "I know we played some young players but that is not an excuse, we expect more of them than that.
"Maybe I should have brought on Paul Scholes and Alan Smith at half-time. If I had been pleading guilty to a murder charge those would be my mitigating circumstances.
"It is hard to get your head around it. We are all very disappointed. If someone had told me before the game it would be 0-0 I would probably have hit them.
"But I will play a much stronger team in the replay and we will not make this mistake again."