Callum Wilson came off the bench to score in stoppage time as West Ham beat Everton 2-1 to stay out of the Premier League relegation zone.
On a topsy-turvy afternoon in the capital, Nuno Espirito Santo's side had appeared to be cruising to a huge three points thanks to Tomas Soucek's 51st-minute header, until late drama.
Firstly, as news of a Tottenham Hotspur goal at Wolves filtered around the London Stadium, Kiernan Dewsbury-Hall volleyed the visitors level with just two minutes to go, pushing the Hammers into the drop zone on goal difference.
But just as the board was raised to indicate there would be another eight minutes of injury time, up popped the ever-green Wilson to score after good work at the back post by Jarrod Bowen, a vital strike that saw West Ham again leapfrog their London rivals in the table.
There had been little indication of the climax we were in store for, though, after a cagey first period in the east London sunshine, only for Soucek's thumping near-post header from Bowen's inswinging corner to spark the game into life.
The home side had appeared to be doing a good job seeing the match out, only for that man Soucek to somehow deflect Thierno Barry's effort on to the bar, before Everton were denied what appeared a convincing call for an 84th-minute penalty when Mateus Fernandes appeared to scoop the ball away with his hand.
Video Assistant Referee Michael Salisbury deemed it accidental, but that close call seemed to cause doubt in the West Ham back line and minutes later Dewsbury-Hall's sweetly struck volley from James Tarkowski's clever headed knock down looked to be a knock-out blow for the hosts.
That was until Wilson used all his experience in the second minute of injury time to know exactly where Bowen's knock down would land as West Ham stayed two points clear of Spurs in the race to beat the drop, with now just four games left to play.
West Ham boss Nuno:
"Nobody is making it easy. It's going to be a big fight, I think, until the end. But the good thing is that we don't give up. We're still on it. The momentum, especially here at the London Stadium, I think it's a huge factor in the Premier League."
Everton boss David Moyes:
"It's not as if the ball comes on to his hand, his arm goes towards the ball [regarding the decision not to award Everton a second-half penalty].
"I think today's the first time I've heard the word 'accidental' being used. I think that word had been taken out of the vocabulary really."
Your Site' Rich Morgan at the London Stadium:
If West Ham do manage to stay up this season, then they will have former manager David Moyes to thank in many ways as it was the Scot who brought both Tomas Soucek and Jarrod Bowen to the club during his time in charge at the London Stadium.
Those two have been pivotal in trying to keep the Hammers in the Premier League and they were at it again in Saturday's vital, last-gasp 2-1 home win against Everton that kept them two points ahead of Tottenham in the drop zone.
It was Soucek who crucially opened the scoring from Bowen's corner, before somehow diverting Thierno Barry's seemingly goalbound strike onto the bar to preserve that slender lead with 12 minutes left to play.
And while Everton did level with just four minutes to go, it was skipper Bowen who set up Callum Wilson for the injury-time winner that may end up keeping West Ham in the Premier League, with Nuno praising his opposite number after the game.
"I think David left a legacy here at the club," said the West Ham boss. "He brought success, he brought trophies. And he did it with Jarrod, with Tomas and some more that are still here in the squad."
