Michail Antonio scored his second winner in four days as his stunner lifted West Ham up to seventh with a 2-1 victory over West Brom.
The lowly Baggies picked up their first win under Sam Allardyce at the weekend and again impressed at the London Stadium, but in the final seconds of a steadfast first half found themselves behind when Jarrod Bowen chested in Vladimir Coufal's cross.
West Ham's return to form has been somewhat longer-term but their 100 per cent start to 2021 looked in jeopardy when Matheus Pereira was allowed to travel to the edge of the box before firing past Lukasz Fabianski five minutes after the restart.
The visitors' hopes of moving within two points of escaping the relegation zone was shortlived, though, with Antonio firing in a superb winner on the turn from Andriy Yarmolenko's header, to lift the Hammers above Chelsea - who visit Leicester later on Tuesday - and into seventh.
West Ham: Fabianski (6), Coufal (7), Dawson (6), Ogbonna (7), Cresswell (7), Rice (7), Benrahma (6), Bowen (7), Soucek (6), Lanzini (7), Antonio (8).
Subs: Yarmolenko (6), Fornals (6), Noble (n/a).
West Brom: Johnstone (6), O’Shea (6), Ajayi (6), Bartley (7), Gibbs (6), Livermore (6), Sawyers (7), Pereira (7), Gallagher (6), Grosicki (7), Robinson (6).
Subs: Furlong (6), Robson-Kanu (6).
Man of the match: Michail Antonio
Antonio provides another Hammer blow
Some early fouls and high-intensity pressing from Sam Allardyce's visitors suggested they had not come to simply sit back and soak up pressure at the London Stadium, and instead Pereira should have tested Fabianski from the first real chance of the game, but turned Callum Robinson's lay-off well over.
The Hammers found life difficult in the final third with West Brom still managing to pack the box when they did find a dangerous position, but should have seen Craig Dawson score his first league goal for the club when he fired wide when unmarked at a corner.
As the half wore in it slowly developed into a case of attack against defence with the Baggies holding firm - but from the last of 10 open-play crosses from the hosts, they finally found a breakthrough, when Coufal returned Aaron Cresswell's ball across the six-yard box, where Bowen nonchalantly chested in with seconds of the opening period remaining.
The Baggies re-emerged a more attacking outfit again for the second period with Pereira, who had been unusually quiet before the break, showing his quality to score his fourth goal in three games.
With Conor Gallagher ahead of him keeping the West Ham defence in two minds, he strode to the edge of the home box before aiming a powerful effort low inside the far post to beat Fabianski.
For a few minutes, the Hammers struggled to regain their composure with West Brom feeling the confidence of their leveller, but without another chance to really test Fabianski their moment soon came and went.
First Manuel Lanzini's effort, cleared off the line by Dara O'Shea, re-asserted the hosts' dominance, before Declan Rice's effort squirmed across the goal-line and away to safety - but a real moment of quality from Antonio, for the second time in as many games, would again prove the winner.
David Moyes had said in the build-up the best was yet to come from his forward, and the 30-year-old showed exactly what the manager meant as he turned on a sixpence to turn Yarmolenko's header, directed behind him, goalwards and into the bottom corner.
In the final minute, substitute Darnell Furlong was given a chance he had to score, with points at such a premium for the relegation-threatened visitors, but he steered his effort wide of the near post - and allowed West Ham to move seventh, after a fourth straight win they were made to work hard to achieve.
What the managers said...
West Ham manager David Moyes told BT Sport: "It wasn't our best performance but it keeps a small run going. We're showing a bit of growth at the whole club, in how we play and what we do, we'd have liked to have played better tonight but I'm not disappointed when we've taken the three points.
"I'd like to dream a lot, but we're humble and understand we're not going to start shouting about things too soon. History has shown we're not always able to back that up; I want to be the one who can back that up and who does make things look better.
"This isn't where I want to be, we want to be competing at the top end."
West Brom boss Sam Allardyce: "I think it's a great effort from the players, but there's those lapse in concentration moments at the back where we've conceded two goals we could have avoided.
"One was less than 10 seconds left before the end of the first half, a bit more concentration on dealing with the clearance at the beginning, and then a ball back in the box, we had enough bodies to deal with it but it was a goal.
"It was a really great response, we started playing and passing the ball a lot better than in the first half, got the goal, but then you have to expect when you're playing a team at home they're going to put pressure on you - and we, unfortunately, faltered again."
Man of the match - Michail Antonio
West Ham have spent some big money on big-name players in recent years. But who remains their most important attacking asset? A £7m winger-turned-striker from Nottingham Forest.
Again, Antonio showed what an asset he is to the Hammers; he has won them four points alone with his goals this week, but his performance against West Brom had so much more to it. Strength, pace, technical ability.
He is the kind of striker few manage to be at this level against Premier League backlines. He should have had an assist for a Lanzini chance at 1-1 but he made sure he got his goal. When he's fit, he's a match for any defence in the league.
- West Ham have won each of their opening four matches of a calendar year for just the second time in their history, last managing to do so in 1958 under Ted Fenton, a run in which they also beat Stockport County in an FA Cup encounter.
- West Brom have now lost 12 of their 19 league games this season; indeed, seven of the last nine sides to have lost at least 12 matches at the halfway stage of a 38-game Premier League season have gone on to be relegated (except Swansea in 2016-17 & Burnley in 2018-19).
- West Ham have picked up 32 points from their 19 league games this season (W9 D5 L5), the Hammers' highest ever points tally at the halfway stage of a Premier League season.
- Tonight's match between West Ham boss David Moyes (564) and West Brom manager Sam Allardyce (518) was the 1082nd Premier League game combined between the two men, the most number of matches between two bosses facing off since April 2018, when Manchester United beat Arsenal (José Mourinho (285) versus Arsène Wenger (825)).
- After 11 matches without a goal in all competitions, Matheus Pereira has since netted in each of his last three appearances for West Brom (4 goals), as many as he netted across his previous 37 games.
- Before taking the West Ham job in 2011, Sam Allardyce had only lost two of his 14 matches against the Hammers; however, since leaving the club in 2015, the now-West Brom boss has suffered defeats in each of his four such clashes - all in the Premier League.
- Each of Michail Antonio's 41 Premier League goals have come from inside the area, with his winner for West Ham his 14th strike at the London Stadium in the top-flight, now the outright most by any player.
- West Brom extend their winless top-flight run on a Tuesday to 33 matches since beating Watford 2-0 in May 1985 (D14 L19); indeed, their Premier League run of 30 games without a win on this day is the most by any side on any given day in the competition's history.
West Ham host Sky Bet League One side Doncaster in the fourth round of the FA Cup on Saturday; kick-off at 3pm.
West Brom, already eliminated from the competition, are back in action next Tuesday when Manchester City visit The Hawthorns; kick-off at 8.15pm.