Match ends, West Ham United 3, Southampton 0.
West Ham manager David Moyes said their fans' support "inspired" his players as they thrashed relegation rivals Southampton at London Stadium to move clear of the relegation zone.
The game was the Hammers' first since fans invaded the pitch during their 3-0 home defeat by Burnley but they produced a brilliant performance to overcome their recent troubles and end a run of three consecutive heavy defeats.
"The supporters were great - they have been great here bar a few," Moyes said.
"The players gave them something to shout about today."
Moyes' side eased the tension around the ground with two goals in the opening 17 minutes, first from Joao Mario and then Marko Arnautovic.
Mario smashed in the opener from the edge of the penalty area after being picked out by Cheikhou Kouyate, who had powerfully carried the ball away on the counter-attack.
Portuguese Mario then set up Arnautovic for the second with a brilliant cross from the right that the Austrian bundled home at the second attempt.
Arnautovic added his second in first-half stoppage time, volleying home another fine cross, this time from the left flank by Arthur Masuaku.
"The players were great. Their prep over the last few weeks, their attitude has been great - they wanted to put past events behind them," Moyes added.
"We think we're good enough to be clear of the bottom three. Recent results haven't been good but we played well."
Southampton were dire in Mark Hughes' first league game in charge and remain in the relegation zone, two points from safety.
Victory for West Ham takes them up to 14th, five points clear of Saints in 18th.
- Relive all of Saturday's Premier League action
- Protests, marches - and three valuable points for West Ham
- How West Ham completed their crucial win
- Arnautovic plays like a man possessed against Mark Hughes - Nevin
Gloom lifted at London Stadium
There were protests outside of the ground and a heavily increased security presence inside, but the difference in the atmosphere from West Ham's previous game was stark.
In toxic scenes during the defeat to Burnley, fans invaded the field, threw missiles and protested against the club's board, but at full-time on Saturday there was a celebratory mood as the crowd gave the players a standing ovation from the field.
West Ham's joint owners, David Sullivan and David Gold, were in attendance but watched the game away from the directors' box where they previously received abuse, although the home fans' passion was channelled in supporting their team throughout as captain Mark Noble had pleaded for before the game.
Moyes' side dominated proceedings, particularly in the first half during which they had nine of their 13 shots, and were fully deserving of their three-goal winning margin.
They outplayed Southampton in central midfield and each goal came from excellent team play.
Mario, on loan from Inter Milan, was a constant threat and Masuaku drove down the left wing at will on his return from a six-game ban while Arnautovic was a clinical spearhead up front.
Arnautovic makes his point to Hughes
Arnautovic celebrated his first goal in the direction of Hughes, who sold the Austrian to the Hammers when in charge of Stoke last summer.
It was his second against a Hughes-managed team this season having also scored in West Ham's 3-0 win over Stoke in December - and he celebrated with crossed arms, a reference to the crossed irons in West Ham's crest.
"They have worked together over the years [Arnautovic and Hughes], Marko is that type," Moyes said.
"People who have worked with him know that, they will tell you."
Hughes said after the game that he wasn't aware of the Arnautovic's gesture.
"My relationship with Marko Arnautovic when I worked with him at Stoke was very good, you'll have to ask him about that [goal celebration]," he said.
"I don't know if he was pointing at me or was just excited by scoring."
Big problems for Hughes and Southampton
Hughes was appointed Southampton manager earlier this month, tasked with achieving Premier League safety in the eight remaining games.
He secured an FA Cup semi-final with victory over Wigan in his first game in charge but in east London oversaw one of Saints' worst performances of the season.
They were toothless in attack and did not force West Ham goalkeeper Joe Hart to make a save in the 90 minutes.
In the first half they had just two touches in the West Ham penalty area and consistently misplaced passes with their passing accuracy at one point below 60%.
They have won just once in their last 18 Premier League matches and five of their remaining seven games are against teams in the top half of the table.
"We were poor," Hughes said. "The opening 10 minutes of any game is key, you have to manage it correctly and we damaged ourselves.
"We conceded poor goals and gave us too much to do."
The Saints welcomed back striker Charlie Austin, who remains the club's top scorer this season despite having not played since December 23, but failed to score for a third league game in a row.
"We have to find a way to score goals," Hughes said.
"If you can't get a foothold in the game by working hard and winning the right to play you are not going to create chances. We have to understand that we are in a situation of our own making."
BBC Sport's Simon Stone at London Stadium:
It is far too simplistic to say all West Ham's problems at London Stadium could be solved by a few wins.
Over a four-hour period before kick-off, I saw a lot of fans - male and female, young and old - vent their frustrations at a variety of issues about the club, from improving the feel of the stadium to getting rid of the owners completely.
But there is no doubt either, what was always going to be a tough transition from the earthy and nostalgic Upton Park to the white, almost corporate London Stadium, from West Ham's traditional home to one they don't actually own, would have been a lot smoother had their form been better here.
Three-nil is not a massive score. But it is the joint record West Ham have achieved in almost two seasons at the stadium. Brighton and Burnley between them have done the same here this season alone.
Once again, the first half proved a winning team can generate an atmosphere too.
Today's result will generate some momentum. For West Ham's sake, they must keep it going.
Man of the match - Marko Arnautovic
Hart's long wait - the best stats
- West Ham United scored three first-half goals in a Premier League game for the first time since September 2012 against Fulham.
- Indeed, the Hammers have scored three goals in a Premier League game at London Stadium for just the second time - also 3-0 against Crystal Palace in January 2017.
- Southampton have won just 28 points from their 31 Premier League games this season - only in 1996-97 and 2004-05 (27 each) have they recorded fewer at this stage of a Premier League campaign.
- Mark Hughes hasn't won his first Premier League match in charge of a club since September 2004 at Blackburn - losing four of his five such games since then (lost with Man City, QPR, Stoke and Southampton, and drew with Fulham).
- Hughes has won just one of his last 12 away Premier League games as manager (W1 D3 L8).
- Joao Mario netted his first-ever Premier League goal in what was his sixth appearance in the competition.
- Joe Hart kept his first Premier League clean sheet since September (versus Swansea), ending an eight-game wait for a shutout.
West Ham travel to Chelsea in their next game on Sunday, 8 April (16:30 BST kick-off) while Southampton face Arsenal earlier the same day (14:15 BST).
- 8KouyatéSubstituted forCullenat 89'minutes
- 30AntonioSubstituted forFernandesat 9'minutes
- 18João Mário
- 7ArnautovicSubstituted forHugillat 80'minutes
- 2Cédric Soares
- 5StephensBooked at 59mins
- 11TadicBooked at 80mins
- 18LeminaBooked at 54mins
- 22RedmondSubstituted forBoufalat 67'minutes
- 10AustinSubstituted forCarrilloat 83'minutes
- 20GabbiadiniSubstituted forLongat 45'minutes
- Jonathan Moss
- Shots on Target
Second Half ends, West Ham United 3, Southampton 0.
Attempt missed. Shane Long (Southampton) header from the centre of the box misses to the right. Assisted by Cédric Soares with a cross.
Aaron Cresswell (West Ham United) hits the bar with a left footed shot from outside the box. Assisted by João Mário following a set piece situation.
Foul by Sofiane Boufal (Southampton).
Mark Noble (West Ham United) wins a free kick on the right wing.
Substitution, West Ham United. Josh Cullen replaces Cheikhou Kouyaté.
Attempt missed. Wesley Hoedt (Southampton) left footed shot from outside the box misses to the right. Assisted by Jack Stephens.
Foul by Pierre-Emile Højbjerg (Southampton).
João Mário (West Ham United) wins a free kick on the left wing.
Substitution, Southampton. Guido Carrillo replaces Charlie Austin.
Attempt missed. Dusan Tadic (Southampton) left footed shot from outside the box misses to the right. Assisted by Sofiane Boufal.
Jack Stephens (Southampton) wins a free kick in the defensive half.
Foul by Jordan Hugill (West Ham United).
Foul by Charlie Austin (Southampton).
Arthur Masuaku (West Ham United) wins a free kick in the defensive half.
Dusan Tadic (Southampton) is shown the yellow card for a bad foul.
Foul by Dusan Tadic (Southampton).
Cheikhou Kouyaté (West Ham United) wins a free kick on the right wing.
Attempt blocked. Pierre-Emile Højbjerg (Southampton) left footed shot from the centre of the box is blocked. Assisted by Sofiane Boufal with a cross.