Manchester United suffered a 1-0 defeat by Championship (second division) side Derby County in the first leg of their League Cup semi-final at Pride Park on Wednesday.
Kris Commons fired the only goal with half an hour gone and Derby could have taken a two-goal advantage to Old Trafford for the second leg in two weeks' time had Rob Hulse not wasted a glorious late chance.
United manager Alex Ferguson fielded an under-strength side but introduced Wayne Rooney and Cristiano Ronaldo late on with the latter almost equalising with a trademark free kick that brushed the post.
Until then the Premier League champions had rarely tested their former keeper Roy Carroll in the Derby goal.
Derby, relegated from the top flight last season with a record low points total and languishing in 18th place in the Championship, had new manager Nigel Clough watching in the stands as he prepared for his first day in charge.
Clough, confirmed as the club's new manager on Tuesday, must have been impressed by the organisation and spirit of Derby who fully deserved their first leg advantage.
United came under pressure early on, with Jonny Evans forced to clear one effort off the line. Andy Todd then lifted a good chance over the crossbar.
The hosts were rewarded for their enterprise when Commons surged into space midway inside the United half and advanced to smash a shot past Tomasz Kuszczak from 25 metres.
United, who host Chelsea in the Premier League this weekend, were subdued throughout, although they will start the second leg as favourites to reach the final.
Holders Tottenham Hotspur beat Championship side Burnley 4-1 at home in the first leg of their semi-final on Tuesday.