West Ham moved outside of the Premier League relegation zone as Nayef Aguerd's first-half header was enough to secure a 1-0 win over bottom-of-the-table Southampton at the London Stadium on Super Sunday.
In a contest littered with individual errors, low on clear-cut chances but laced in significance, it was David Moyes' side who would prevail to increase the pressure on Saints, who still sit only three points adrift of safety.
The hosts took a lead they would not relinquish in the 26th minute after a lengthy VAR review ruled Aguerd was onside when he headed in a free-kick from Thilo Kehrer.
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It required three minutes and 48 seconds - the longest VAR delay of the season - for referee Paul Tierney to be informed by Peter Bankes that the goal should stand after a tight offside call.
Jarrod Bowen struck the woodwork with a sublime effort before the interval, but one goal would prove enough to overcome a blunt Saints side who went closest to equalising when substitute Paul Onuachu headed against the bar in the final five minutes.
The result moves West Ham up to 14th in the table, but only a point above Everton in 18th place as they extended their unbeaten home run in 2023 to six matches.
"I'm really pleased about the result," said Moyes. "We've played much better in the past and not won but today was all about the result. Unfortunately we've had that quite a lot already this season. The players have dealt with the pressure and anxiety we've had.
"Mainly because of playing on Thursdays and we've had games in hand. With having to play catch-up, that can make it a bit nervy and we were today."
Reprieve for Moyes as Hammers edge six-pointer
Moyes spent the international break in the relegation zone and the Scot will hope this result now acts as a springboard heading into a hectic month of nine fixtures across the Premier League and in Europe. It is the highest the Hammers have been in the table this season since November 5.
West Ham's domestic form has been in stark contrast to their run in Europe, having reached the quarter-finals of the Europa Conference League with 10 straight wins.
But Moyes, who retains the backing of the club's owners despite their struggles, witnessed a morale-boosting win that moved his side up five places in the table.
After a typically anxious opening 26 minutes in which neither side truly asserted any degree of dominance, West Ham struck from a set piece, Saints' Achilles' heel all season.
Kehrer's deep delivery from the right was met by the leaping Aguerd, his header precise and back across goal. The VAR lines were drawn and they would eventually favour the hosts.
Southampton have now conceded 13 goals from set pieces in the Premier League this season - only Bournemouth have conceded more (17). Indeed, the Saints also lead the league in 2022/23 for headed goals conceded (12).
Romain Perraud immediately stung the gloves of Lukasz Fabianski on his return in goal for West Ham after a five-game absence but the hosts might have doubled their lead before the break when Bowen's curled effort came back off the crossbar.
The Saints headed to the London Stadium bottom of the table but only two points from safety, and they began the second period sprightly with Romeo Lavia and the substitute Carlos Alcaraz testing Fabianski.
Moyes said his players were ready to fight for their Premier League lives, but they showed composure alongside the necessary battling qualities to manage their opponents.
Since Ruben Selles replaced Nathan Jones during February, Southampton had taken eight points from his six previous league matches - but despite his best effort to find solutions, Onuachu's header against the crossbar was as close as they would come.
With nine clubs all looking set to battle it out for their top-flight status, the fight for survival appears set to be one of the tightest of recent seasons. These precious three points for Moyes, and for West Ham, could prove pivotal come the final reckoning.
Moyes: A deserved victory
West Ham boss David Moyes:
"We've beaten Everton and Nottingham Forest while we've drawn with Chelsea and Aston Villa before this so the home form has been good. We've been in good form more or less since the World Cup, including in Europe.
"We've felt ourselves catching up. There have been some shocks and some surprising results of late and that is due to the quality across the Premier League.
"I hope none of you are betting because if you are, you're probably not winning many of them given how the results have gone! There's not an awful lot between many of the sides in this league.
"We didn't start the game well but we then got the goal which meant we had something to hang onto. Overall, I think we just about edged the game and deserved the victory."
Selles rues set-piece failure
Southampton boss Ruben Selles:
"It is always frustrating when you concede a goal but especially from set plays, and when you lose by it. Sometimes, the VAR decisions are for you and other times they aren't. It was very tight.
"It shouldn't affect our mindset. We need to be stronger in these situations. It wasn't the four-minute wait for the goal to be awarded, but the goal itself which affected our mentality.
"Set pieces is a part of the game we've not been good at this season and we need to step up during the coming games.
"I'm focused on the performance and what we are doing, no matter who the opponent is. I feel we can perform better, especially in moments like today with the goal. In some games, we've managed to keep the clean sheet and this is the basis to get something.
"We cannot spend our energy looking at the relegation picture and what we cannot affect. I cannot affect the other games and results. What I can do is elevate the spirit of my players to face Manchester City next and that is my focus."
Analysis: Far from pretty but absolutely priceless
Sky Sports' Ben Grounds at the London Stadium:
West Ham had a three-week break owing to their fixture with Manchester City being postponed and the subsequent European Championship qualifiers, which gave David Moyes' and his backroom staff a chance to take stock ahead of a hectic schedule.
This was the first of nine games for the Hammers in April, with the majority of them at home and the away visits not too taxing in terms of travel.
Such has been the interrupted nature of this campaign, West Ham could still play as many as 17 more games. There is plenty to play for both in the Premier League and in Europe.
After results on Saturday conspired to leave them second from bottom, Aguerd's first-half header rocketed them to the heady heights of 14th and help build the momentum Moyes craves.
'Must-win' games have been a regular occurrence for the under-pressure Moyes this season, but just as they had done against Everton and Nottingham Forest recently, his team pulled out a victory when they needed it most.
With Leicester the latest club to swing the axe - the news of Brendan Rodgers' departure filtered through during this match - only Moyes and Steve Cooper at Forest of the bottom nine sides have kept their jobs this season.
West Ham's latest win was far from pretty but it was absolutely priceless. The Hammers are breathing a little easier, albeit only two points above the drop zone, but they can put further daylight between themselves and the bottom three at home to Newcastle on Wednesday.
Player of the match - Nayef Aguerd
Morocco defender Aguerd steered a beautifully-controlled header into the net and, after an agonising three-minute VAR review for offside, the goal was given.
It was a first goal for the club for Aguerd - who missed the first half of the season through injury - and it lifted the mood in the London Stadium instantly.
Aguerd's intervention was West Ham's first effort on goal in the game. Indeed, the Moroccan is their 165th different scorer in the Premier League, at least three more than any other side.
Moyes said: "I think it was only the second or third game Aguerd and Kurt Zouma have been able to play alongside each other this season. The performance is important but the result is the most important thing, and hopefully we improve on that as we go along."
Hammers' home comforts - Opta stats
- West Ham are now unbeaten in each of their last five Premier League games at the London Stadium (W3 D2), keeping a clean sheet in all three victories during that run.
- Southampton have failed to win any other their last six Premier League games in which they've conceded the opening goal (D1 L5), with the Saints failing to score in any of those five defeats.
- Only Bournemouth and Crystal Palace (both 13) have failed to score in more different Premier League games this season than Southampton (12), with them failing to score in three successive away games for the first time since October.
What's next?
West Ham are back in action in midweek as they host Newcastle on Wednesday night, kick-off 8pm.
A trip to Fulham is on the agenda next weekend, before attention turns to their Europa Conference League quarter-final matches against Gent, which come either side of a home game against Arsenal on April 16, live on Sky Sports at 2pm.
Southampton's next game is a Saturday Night Football clash at home to Manchester City, live on Sky Sports with kick-off at 5.30pm.
The Saints also face tricky matches away at Arsenal and Newcastle in April, but their home games are against fellow relegation rivals Crystal Palace and Bournemouth this month.