Manchester United boss Sir Alex Ferguson apologised to fans for his team's display in their 2-1 Carling Cup quarter-final loss to Crystal Palace.
Glenn Murray headed the winner for the Championship side in extra-time.
"I don't know where to start to be honest," said Ferguson. "My apologies are to the fans because that was not a Manchester United performance.
"I don't want to take anything away from Crystal Palace," he added. "I am just very disappointed."
Ferguson continued: "I wish them every success and hope they get to the final because it was a fantastic, mammoth effort from them tonight.
"Every one of their players worked their socks off to try to get to the semi-final."
Palace took the lead through a stunning swerving strike from Darren Ambrose on 65 minutes but United looked the most likely to progress after Federico Macheda replied from the penalty spot.
But Palace forced the game into extra-time and grabbed the winner with a Murray header from an Ambrose free-kick.
Substitute Murray looked marginally offside when the cross came in, and Ferguson was convinced the goal should not have counted.
"Obviously the goal was offside - the second goal - from what I have seen," he said.
"We are not getting any luck from linesmen just now but I can't take that away from Crystal Palace. They fought hard to get the result and they deserve it."
Palace manager Dougie Freedman, who took over the cash-strapped club midway through last season, praised his team for a superb collective effort against the Premier League champions.
"They should be proud of themselves," he said. "They stuck together and I think that was a really good cup tie between two teams who gave everything.
"In the last 15-20 minutes of extra time the desire shone through in the end.
"That is what they should be proud of. Sir Alex has a wonderful team, they kept on going.
"We had to dig in and show that hunger and desire to see the tie through and that is what they have done.
"There was no tactical genius. We had to dig in. I felt we had a good gameplan and I thought every single player stuck to our gameplan."
Palace avoided Premier League big guns Manchester City and Liverpool to draw fellow Championship side Cardiff in the semi-finals, but Freedman still expects a huge challenge.
"It's probably the hardest draw, to be honest," he said. "They are up at the top of the Championship and it is going to be very difficult for us.
"But I am just proud of the lads, to get through to the semi-finals from where we have come from in the last couple of years - relegation zones and administrations.
"We will enjoy tonight and approach that when it comes along."