Scott McTominay fired Manchester United into the FA Cup quarter-finals as Ole Gunnar Solskjaer's men edged past West Ham in extra time.
The Red Devils reached the final four last season - one of four successive semi-final cup competition exits - and progressed from a tough fifth-round clash on Tuesday evening.
Ex-United boss David Moyes' West Ham side made life difficult on a bitterly cold night at Old Trafford, where substitute McTominay struck home Marcus Rashford's lovely 97th-minute lay-off to seal a 1-0 extra-time win.
Solskjaer will be relieved his team made it through to the last eight on a night in which Lukasz Fabianski tipped a deflected Victor Lindelof header onto the post in a first half that they edged.
West Ham had already been hit by an injury to Angelo Ogbonna at that point and his replacement Issa Diop became the first concussion substitute in English football when withdrawn at half-time.
Andriy Yarmolenko was then forced off in a goalless second half as the match went to extra time, with McTominay firing in his seventh goal of the season to seal progress.
West Ham were able to call on Tomas Soucek after his red card against Fulham was rescinded, while United made six changes from Saturday's frustrating 3-3 draw with Everton.
Two of those introductions combined well for the first chance of the evening as Alex Telles slipped through Anthony Martial to get away an 11th-minute effort.
Ogbonna got in the way of the shot but could not continue afterwards, having been sandwiched between the forward's boot and oncoming goalkeeper Fabianski.
The defender had several minutes of treatment before being replaced by Diop, with Aaron Cresswell throwing himself in front of a Mason Greenwood strike at a time when the Hammers were temporarily down to 10 men.
Nemanja Matic lashed over as United penned the visitors back, with Fabianski reacting superbly to push a Lindelof header onto the post after taking a deflection off Craig Dawson.
Donny Van De Beek saw a shot deflected over towards the end of a first half in which Diop and Martial required treatment after a nasty clash of heads.
The defender continued for the remainder of the opening period but came off at half-time, with the Hammers confirming on their match blog that he was "replaced as a concussion substitute".
Ryan Fredericks came on for him and Ben Johnson replaced Jarrod Bowen as the visitors went to a back five, with Yarmolenko soon limping off injured to be replaced by former Ireland underage international Mipo Odubeko.
Odubeko, who joined West Ham from United, had some decent touches but was working off scraps up front and was replaced with eight minutes left in extra-time.
There were more substitutions to report on than clear-cut shots, with Fabianski doing well to thwart Rashford's close-range shot in a drab second period.
West Ham were showing a little more intent at the other end, but Aaron Wan-Bissaka was the first person to force Dean Henderson into action after horribly mis-hitting a clearance.
Bruno Fernandes and McTominay were brought on in the 73rd minute, with the former seeing a strike deflect over before Edinson Cavani came on to add extra bite.
Both sides struggled to stamp their authority on the game and Dawson wasted a chance to snatch victory in stoppage time, failing to get clean contact on a corner as Wan-Bissaka cleared his header.
The match went into extra time as a result, with Brandon Williams and Luke Shaw introduced by United.
The latter quickly made an important contribution, winning the ball after Declan Rice's heavy touch to start the match-winning move. West Ham failed to effectively deal with a cross and Rashford teed up McTominay delightfully to rifle home in the 97th minute.
Said Benrahma looked lively as West Ham pushed to draw parity, with the substitute glancing a header straight at Henderson in the second half of extra time.
Martial wasted the chance to add gloss at the death but victory was already assured. West Ham created next to nothing although Craig Dawson failed to connect with a header in front of goal in the last seconds of normal time.