Jonathan Spector's Manchester United career ran to just two Premier League starts and ended four years ago but the US international finally made his presence felt at the Old Trafford club with two first-half goals last night that ended a 29-game unbeaten run for Sir Alex Ferguson's side.
Spector's goals – the first and second of his career – were followed by two second-half efforts from Carlton Cole to complete an emphatic home victory that secured West Ham's place in the semi-finals of the Carling Cup for the first time in 21 years and ended United's hopes of winning the competition for a third season in a row.
And while Avram Grant was allowed to reflect on the possibility that the momentum from this win might spill over into West Ham's league form, Ferguson conceded that the manner of his side's defeat exposed the weaknesses in his youthful back-up players.
Both managers made changes to their starting line-ups – six from Grant, 10 from Ferguson – but it was clearly the visitors who suffered most.
Apart from a brief period at the very start of the game, United were repeatedly pulled apart with centre back Jonny Evans enduring a particularly difficult time.
"I didn't expect that for sure," Ferguson said. "If you analyse it, the goals we gave away were too soft. We had all the young players and it's probably a lesson. They were terrible goals for us. We had a few half chances and one or two bits and pieces but really the goals killed it. You just can't give goals away like that.
"They were poor goals. And [the players] are too young to carry these kind of mistakes and still win. We invest in youth and we have always done that and they will remember this. They will come on from it. Unfortunately it was a quarter-final tie and it could have been a really good opportunity of winning the cup again."
Yet if the result was unexpected, then Spector's contribution, on his first appearance since August, was even more surprising. Similarly, Cole's contribution could hardly be described as predictable with the England forward making the most of a rare starting opportunity to score only his second and third goals of the season, his first double in a game for eight years.
"Before the game, I didn't think we would do this," said Grant. "I thought we could win but not by this score."
Clearly benefiting from an injection of confidence after Saturday's victory over Wigan, Grant's side quickly exposed the visitors as United-lite, overpowering the Premier League leaders who struggled to find fluency.
The greatest threat came from Victor Obinna, whose pace and trickery unsettled the right-hand side of the United defence, and it was the Nigerian's powerful 16th-minute shot that provided the first indication of the direction the game would take.
West Ham were convinced that Obinna's effort had earned them an early lead but the ball had clipped Spector's heel on the way into the net after the US international had drifted into an offside position. The home celebrations erupted but referee Mark Clattenburg – in charge of his first United game since allowing Nani's controversial goal against Tottenham on 30 October – noticed his assistant had flagged and ruled out the strike.
Ferguson believed that was the game's turning point and he was right. West Ham's frustration was allowed to fester for just six minutes before Spector converted legitimately, this time when he got across Evans and directed his header beyond Tomasz Kuszczak.
Spector was clearly enjoying his unfamiliar role in midfield and his willingness to get forward also brought about his second goal. The American started the move near halfway and his persistence ensured he was on hand inside the United box when the ball broke free after Obinna had attempted to work an opening.
Obinna was again the dominant figure after the break and the Nigerian contributed the assist for West Ham's 56th-minute third, delivering a left-wing cross that was met by Cole's head.
Cole's second followed quickly when Obinna teased substitute Rafael Da Silva before delivering a low ball into him. The forward still had work to do, but he easily turned Evans before converting with his left foot.
West Ham United (4-4-2): Green; Ben-Haim, Tomkins (Reid, 74), Upson, Spector; Faubert, Barrera (Hines, 76), Boa Morte, Kovac; Cole (Stanislas, 89), Obinna. Substitutes not used Boffin (gk), Reid, Parker, McCarthy, Piquionne.
Manchester United (4-4-1-1): Kuszczak; Smalling, Fabio (Rafael, 65), O'Shea, Evans (Brown, 72); Anderson, Giggs, Fletcher, Bebe (Macheda, 46); Hernandez; Obertan. Substitutes not used Amos (gk), Park, Carrick, Eikrem.
Referee M Clattenburg (Tyne & Wear).