Marcus Rashford and Marouane Fellaini spoiled West Ham's final FA Cup match at Upton Park as Manchester United moved into the semi-finals with a 2-1 victory.
Rashford sparked the quarter-final replay into life after 54 minutes with a stunning piece of quality to beat Darren Randolph, before Fellaini bundled home a second to set up a last-four meeting with Everton a week on Saturday.
There was little to separate the two sides in the opening 45 minutes, but, just before the hour, Rashford profited after excellent work from Anthony Martial, curling an 18-yard effort off the underside of the bar.
Martial was at the heart of the visitors' second, too, as his shot was turned beyond Randolph by the unmarked Fellaini.
Two goals in quick succession sapped the life out of West Ham, and, although James Tomkins pulled one back and Cheikhou Kouyate had a late header disallowed for offside, Slaven Bilic's men could not find an equaliser, leaving them to focus on challenging the top four in the Premier League.
With the backing of their vociferous home support, West Ham, who relocate to the Olympic Stadium at the end of the season, had the better of the opening 10 minutes with crisp passing moves, Dimitri Payet and Aaron Cresswell particularly impressing on the left.
Chances were hard to come by, though, with only Enner Valencia bringing a save out of David de Gea, his low shot from Cresswell's pass easily held by Spain's number one.
Slowly the visitors found their footing and began to pose a threat on the counter, Fellaini seeing a glorious chance deflect off Angelo Ogbonna before Randolph pushed it over.
Manchester United finished the half the stronger and saw two opportunities go begging. Jesse Lingard fired straight at Randolph after a marauding run by Rashford, before Michael Carrick's low shot fizzed wide from 20 yards.
The visitors continued to press after the restart and soon took the lead as teenage prodigy Rashford netted his sixth goal in all competitions this season.
After Martial had intercepted a loose Michail Antonio pass, the Frenchman found the 18-year-old and - after making space for himself - he curled a pinpoint effort into the top corner.
Smart goalkeeping from Randolph kept the home side from being cut adrift in the tie as he raced off his line to intercept before Lingard and Rashford could pounce.
Randolph could do nothing to stop a second goal for Louis van Gaal's men, though, as Fellaini diverted the ball home after 67 minutes. The Belgium international bundling home Martial's deflected shot from close range.
That two-goal advantage did not last long, however, as Tomkins halved the deficit with 11 minutes to play. The defender pouncing from two yards out to head home Andy Carroll's knock down.
Carroll and Kouyate went close to taking the game into extra time in the closing seconds, but both found De Gea in sensational form, the latter also seeing a header ruled out for offside.
Manchester United introduced Wayne Rooney for his first appearance in two months with a minute to play, and he was able to help them secure a semi-final berth, easing the pressure on Van Gaal following a lacklustre campaign that could yet end with silverware.