West Ham boss Manuel Pellegrini said he was "ashamed" of his team after League One strugglers AFC Wimbledon delivered an FA Cup fourth-round shock to his Hammers in a gripping tie in south-west London that ended 4-2 on Saturday.
Wimbledon, bottom of England's third tier, took full advantage of a lacklustre West Ham display with Kwesi Appiah putting them ahead before Scott Wagstaff's expertly-taken double, the first a cool finish and the second a volley, either side of halftime put them 3-0 up against Manuel Pellegrini's side.
West Ham, who made six changes from their last Premier League game against Bournemouth, finally responded with Lucas Perez firing home and then Brazilian substitute Felipe Anderson curling home a free kick.
With 20 minutes remaining it seemed West Ham would overhaul their modest hosts but AFC Wimbledon absorbed some intense pressure before substitute Toby Sibbick headed past Adrian in the 88th minute to send them into the fifth round for the first time since the club was formed in 2002.
West Ham are 58 places higher than AFC Wimbledon in the English football pyramid.
AFC Wimbledon were formed by fans of former FA Cup winners Wimbledon who controversially uprooted from London to Milton Keynes in 2002 and became MK Dons.
After working their way through the minor leagues they rejoined the Football League in 2011 but Saturday's victory revived memories of the club's roots.
It was the only time that AFC Wimbledon have progressed from an FA Cup tie against a side from a higher division.
Manager Wally Downes, part of the original Wimbledon who won the 1988 FA Cup but 14 years later moved to Milton Keynes, said his side had been hanging on desperately.
"When you are 3-0 up against a Premier League side you can't think you will be better than them and you have to combat the period you know they will have," he said.
"Luckily enough we got the fourth. It happens in all games -- at 1-0 up it is human nature to try and hang on to what you have. Players want to sit back and stick with what they've got.
"We were running short of legs at the time and Toby Sibbick is a terrific athlete and managed to get himself right up there to get the fourth."
West Ham boss Pellegrini criticised his side's attitude.
"It's very easy to explain what happened -- it was one team who wanted to win and another team who played without any desire or any ambition to win or continue in this cup," he said.
"In the first 45 minutes, we didn't fight."
He added: "Was I angry at half-time? Yes of course. I was ashamed of them.
"I didn't expect it, the attitude, playing against a team that sits two divisions below us, but in football, you can lose in two or three balls.
"They started the way we needed to start and when you have such high pace with the quality of the players and we didn't have the same level."
Press Association contributed to this report.