A howler from David de Gea gifted West Ham victory over Manchester United to boost their chances of Premier League survival and deal a blow to the Red Devils' top-four hopes.
De Gea let a tame Said Benrahma effort from distance slip through his grasp to put the Hammers in front midway through the first half.
The win moved David Moyes' side seven points clear of the relegation zone with a superior goal difference to all the sides below them.
Fourth-placed Manchester United missed the chance to move above Newcastle into third as they remain just a point ahead of Liverpool in fifth, with a game in hand.
Tomas Soucek twice went close for the home side after the break as they pushed for a second, while Michail Antonio had a goal disallowed for a foul on De Gea.
Marcus Rashford and Antony both struck the post early on for the visitors, who started the brighter of the two teams but faded after the opening goal.
Substitute Anthony Martial came closest to an equaliser in stoppage time, but Lukasz Fabianski palmed away his rasping effort from a tight angle.
De Gea error opens door to top-four rivals
David de Gea has saved Manchester United on plenty of occasions during his 12-year career at Old Trafford, but his terrible error at the London Stadium has just opened the door for their rivals looking to pip them to a Champions League qualification spot.
Benrahma was surrounded by three Manchester United players and without a team-mate in sight when he attempted a hopeful effort from distance, but De Gea appeared to lose his footing before allowing the ball to slip from his grasp and into the net.
His reaction said it all, with the Spaniard lying face down on the turf as the West Ham fans erupted.
With Liverpool and Tottenham both winning on Saturday and Brighton playing the first of their three games in hand on Monday, Erik ten Hag's side now find themselves under pressure to cling on to a top-four spot with four games still to play.
The visitors had actually started the brighter of the two sides before the opening goal but lacked a cutting edge, having 10 shots without hitting the target before Christian Eriksen finally found Fabianski's gloves in first-half stoppage time.
Their energy levels dipped in the second half, with their only real opportunities a Rashford shot tipped over from a tight angle before Martial went close late on.
Their tame finish to the match suggests their relentless schedule, in which they have played 57 matches already this season, may be taking its toll.
Europe next for Hammers with safety all but secure
This is the perfect start to a huge fortnight for West Ham, who face a two-legged Europa Conference League semi-final against Dutch side AZ Alkmaar either side of a Premier League trip to London rivals Brentford.
Like Manchester United, the Hammers have had a long and hard season, with their exploits in Europe meaning this was their 51st match of the campaign.
But after a slow start, they put in a performance full of zeal and verve that suggests there is plenty of energy left in the legs for the closing weeks of the season.
Although not technically safe, it would take an extraordinary set of results for them to get dragged into the bottom three, meaning they can fully focus on trying to reach a first European final since 1976.
They were excellent in the second half as they took the game to Manchester United, driven on by the superb Declan Rice, who showed no ill effects of the sickness big that caused him to miss the midweek defeat at Manchester City.
It was also a satisfying night on a personal level for Moyes, who secured his first victory over Manchester United since he was Everton boss in 2012, a year before he succeeded Sir Alex Ferguson at Old Trafford.