Alejandro Garnacho again proved to be Manchester United's match winner as he took centre stage in front of the Stretford End.
The Red Devils looked like they were going out of the FA Cup with 20 minutes remaining, but the hosts showed huge character to come back and keep their momentum going following Sunday's Carabao Cup at Wembley. The young Argentine has already come up with the goods late on this season and showed great quality to bend home the winner.
Said Benrahma put the Hammers in front at Old Trafford as the Premier League strugglers threatened upset the status quo by knocking out Erik ten Hag's side. Casemiro, who began on the bench alongside the likes of Marcus Rashford, thought he'd come up with another big moment when he nodded home.
VAR denied him, but United's equaliser didn't come long after as Nayef Aguerd put through his own net from a corner. The pressure continued to come and the hosts looked destined to find the winner, which came with seconds of normal time remaining. Fred added a third in stoppage time after a West Ham error.
Here are five talking points from Old Trafford.
1. Another test passed
A trophy on Sunday underlined United's forward trajectory and their late, late show at Old Trafford was further evidence of their rise. West Ham were 15 minutes away from a major upset as they eyed a notable Old Trafford win following Benrahma's stunning finish.
United though, for so long known for their late goals, proved that they still have their sights on a unique quadruple as they advance into the last eight of the FA Cup. Like all good teams, they were able to put a poor opening 45 behind them to turn the game around.
Ten Hag rang the changes in the second-half and the likes of Rashford and Casemiro underlined their worth by inspiring a period of dominance that always looked like it would end with United grabbing the winner - and Garnacho was the man to deliver it.
2. In or out?
Well, according to VAR, it was in. The contentious moment of the match came early in the second-half when Benrahma fired home for the visitors. He was afforded time and space in the box, owing largely to the United players stopping when they thought the ball had gone out.
The U6 phrase of 'play to the whistle' comes to mind, but the West Ham faithful were forced to wait as the United players appealed. VAR's various angles couldn't prove that the ball had gone out and the Hammers finally converted one of their opportunities - not before time too after they'd spurned several first-half chances.
3. De Gea's big night
The Spanish goalkeeper was one of the few members of the squad to have tasted success at the club prior to Sunday's winaAt Wembley. On a personal note though, the victory in London was that bit sweeter as he made history by registering another clean sheet.
His shutout at Wembley was his 181st since moving to Old Trafford - surpassing the record previously held by Peter Schmeichel. He was presented with an award pre-match by Sir Alex Ferguson, the man who signed him. Much is made of De Gea's future with his contract winding down, but the Spaniard proved he still has it with a vital first-half to save to deny Michail Antonio, who had been sent clear with the game goalless.
4. The Rashford drop off
Big players are inevitably missed when they don't play, but United's reliance on Rashford seems to grow by the week. The England international, who is enjoying his best ever season in front of goal, has been electric since the World Cup but was afforded a rest on Wednesday.
Boy did it tell. Without his injection of pace and energy, without his ambition there was a notable decline in United's attacking output. Anthony Martial has been a big miss given his pre-season form whilst the sudden departure of Cristiano Ronaldo, albeit he was rarely playing, changed the dynamics of the United attack.
Nevertheless, for a side with ambitions of claiming more silverware, possibly this season, the absence of their leading scorer cannot have as much of an impact on their attacking threat as it did. It speaks volumes that, within minutes of United going behind, the main man introduced.
5. Antony's struggles continue
It seems like the harder he tries the less productive he is. Now halfway into his debut season, questions are understandably being asked due to his transfer fee, which heightened expectations. The Brazilian's need to cut in continues to make defenders' jobs easier.
Antony continues to show nice touches, but his final decision - be that a shot or a cross - continues to lack quality. Ten Hag has kept backing his summer signing, but isn't afraid of a big decision. Jadon Sancho is again an option and Antony's grace period will not last forever if he doesn't begin to contribute more regularly and his withdrawal before the hour mark is a fair reflection on his current form.
