Match ends, Arsenal 2, Southampton 0.
Arsenal punished struggling Southampton with two first-half goals to move back into the top four of the Premier League.
The Gunners led when Alexandre Lacazette reacted quickest to turn in Henrikh Mkhitaryan's shot, with the Saints' claims for offside proving futile.
And they doubled their lead shortly after when Mkhitaryan drilled a shot into the bottom corner.
Arsenal should have scored more in a dominant first half, but ultimately it mattered little as those goals were enough to move Unai Emery's side above Manchester United, who drew at home to Liverpool.
Saints, who missed good chances through Nathan Redmond and Matt Targett before each of Arsenal's goals, offered more resistance after the break.
But they remain in the bottom three, a point adrift of fourth-bottom Cardiff, after failing to win for a fourth successive league game.
Do Arsenal need to be more ruthless to secure top-four finish?
Arsenal have struggled for consistency under Emery in the second half of the season, alternating between wins and defeats in each of their 10 previous matches before Southampton's visit.
In truth, anything other than a home win against the Saints looked unlikely. However, Emery may be concerned with his side's inability to demolish their lowly opponents.
The Gunners looked potent every time they burst forward, particularly in the first half, and in the closing stages, against a Southampton side which looked fragile at the back.
Lacazette was allowed the space to turn in the opener, with the visitors' defence unorganised and too concerned about appealing for offside, for his 13th goal of the season.
After Mkhitaryan doubled the lead, the France striker should have added another but somehow scooped over the bar from a few yards out.
Arsenal's dominance was illustrated by the 11 shots which they attempted in the first half, nine of which came from inside the Saints area.
After the break they failed to assert themselves in a similar fashion, until Pierre-Emerick's Aubameyang's introduction as a late substitute stretched the visitors again.
The Gabon striker was unable to add to his 18 goals for the season, tamely side-footing at Saints keeper Angus Gunn from close range and seeing another effort blocked by Jannik Vestergaard's sliding challenge.
Ultimately, they still had enough to see off Southampton, but are likely to need to be sharper in the final third if they are to stay ahead of United and Chelsea to secure a return to the Champions League next season.
That is also particularly pertinent as, despite keeping a rare clean sheet, they still needed keeper Bernd Leno to be alert to prevent Southampton finding a foothold in the game.
Defensive errors cost Saints
Saints manager Ralph Hasenhuttl announced his arrival in the Premier League when his new side caused an upset by ending the Gunners' 22-match unbeaten run in December's reverse fixture.
But momentum has stalled under the Austrian in recent weeks, with Saints' inability to take victory against Crystal Palace, Burnley or Cardiff City proving particularly damning.
Those three fixtures - which included home games against Palace and Cardiff - had been earmarked by Saints fans as ones where they needed to accumulate points to help their bid in avoiding the drop.
Yet only two points from that run proved disappointing and heaped on more pressure for the trip to the Emirates.
Hasenhuttl decided to play Redmond in a lone striking role and that almost paid dividends early on when the former England Under-21 international used his pace to race clear of the Arsenal defence.
However, Redmond could not beat Leno - who stood up to block with his chest - and Arsenal punished them through Lacazette a matter of seconds later.
It was a similar story with the Gunners' second goal, Targett seeing a low angled drive pushed clear by Leno before the home side doubled their lead through Mkhitaryan shortly after.
Both goals were preventable - with a couple of defenders reacting too slowly for the first and a miscued backpass from Jack Stephens punished for the second.
Hasenhuttl reacted by introducing two strikers at the break - Charlie Austin and Michael Obafemi - and taking off Stephens, changing shape to shore up the visitors defensively.
Saints offered more attacking threat, with James Ward-Prowse and Austin going close, but ultimately they could not find a breakthough to worry Arsenal.
Now they turn their attention to Wednesday's crunch relegation battle against second-bottom Fulham - where defeat will leave either side even deeper in trouble.
'The good thing is we didn't collapse' - post-match reaction
Arsenal manager Unai Emery: "I think we deserved to win. We got the chances, we played very well and I think we can do more [to make a] difference to the result in the final 20 minutes of the first half.
"The second half was maybe an under-performance from the first, but I think also we deserved another goal.
"It's difficult to keep the intensity for 90 minutes, in the second half we continued with finding attacking moments and creating chances. The most important is the three points at home with our supporters.
"We are thinking it's a good step and it's game by game. Now we are happy, we are at the moment in this position and we carry on."
Southampton manager Ralph Hasenhuttl: "The key moment was the chance for 1-0 and then they [Arsenal] were up. They were much better and played very simple and we had problems to defend, which is why we switched and changed the shape.
"We had a few chances but Arsenal also did too. If you are 2-0 here then its easy for Arsenal. The good thing is we didn't collapse today. We didn't, but we deserved to lose today.
"For us every game is big. The next weeks are very tough for us and against Fulham we need to have a win and recover very well now for Wednesday and do everything to win this game."
Man of the match - Granit Xhaka (Arsenal)
Why Saints must hate going to Arsenal - the stats
- Arsenal are unbeaten in their last 24 home league games against Southampton - winning 18 and drawing six - since a 1-0 loss in November 1987.
- Southampton have not won any of their 20 away Premier League games against Arsenal, drawing five and losing 15 - the most a team has played away at another without ever winning in the competition.
- Since losing 2-0 against Manchester City on the opening weekend, Arsenal have remained unbeaten in 13 Premier League home games (W11 D2), winning the last seven in a row.
- Southampton have lost seven of their last nine Premier League trips to London and are winless in the last four.
- Alexandre Lacazette has scored against 18 of the 22 Premier League teams he has faced with Arsenal.
- Lacazette is the first Arsenal player to score in four consecutive Premier League games since Robin van Persie in March 2012 (five games).
Both teams are back in Premier League action at 19:45 GMT on Wednesday.
Arsenal host 10th-placed Bournemouth as they aim to earn an eighth-straight home win in the Premier League.
Saints, meanwhile, face second-bottom Fulham in a crunch relegation battle.
- 12LichtsteinerSubstituted forKoscielnyat 56'minutes
- 8RamseySubstituted forÖzilat 63'minutes
- 17IwobiSubstituted forAubameyangat 75'minutes
- 22D Suárez
- 5StephensSubstituted forAustinat 45'minutes
- 17S ArmstrongSubstituted forObafemiat 45'minutesSubstituted forElyounoussiat 65'minutes
- Graham Scott
- Shots on Target
Second Half ends, Arsenal 2, Southampton 0.
Attempt missed. Mohamed Elyounoussi (Southampton) right footed shot from outside the box misses to the left. Assisted by Pierre-Emile Højbjerg.
Corner, Southampton. Conceded by Bernd Leno.
Attempt saved. Matt Targett (Southampton) left footed shot from outside the box is saved in the top left corner.
Corner, Southampton. Conceded by Shkodran Mustafi.
Attempt blocked. Pierre-Emerick Aubameyang (Arsenal) right footed shot from the centre of the box is blocked. Assisted by Mesut Özil.
Granit Xhaka (Arsenal) wins a free kick in the defensive half.
Foul by Pierre-Emile Højbjerg (Southampton).
Corner, Arsenal. Conceded by Jan Bednarek.
Corner, Arsenal. Conceded by Jan Bednarek.
Pierre-Emerick Aubameyang (Arsenal) wins a free kick in the defensive half.
Foul by Yan Valery (Southampton).
Offside, Arsenal. Sokratis tries a through ball, but Pierre-Emerick Aubameyang is caught offside.
Lucas Torreira (Arsenal) wins a free kick in the defensive half.
Foul by Mohamed Elyounoussi (Southampton).
Offside, Arsenal. Granit Xhaka tries a through ball, but Sead Kolasinac is caught offside.
Attempt blocked. James Ward-Prowse (Southampton) right footed shot from the right side of the box is blocked. Assisted by Pierre-Emile Højbjerg with a cross.
Foul by Granit Xhaka (Arsenal).
Charlie Austin (Southampton) wins a free kick in the attacking half.