Arsenal failed to take the opportunity to close the top-four gap as Jan Bednarek's first-half goal plus an inspired display from goalkeeper Fraser Forster gave Southampton a 1-0 victory
The Gunners knew a victory would move them level on points with rivals Tottenham, who , but they could not find a way past Forster and instead suffered their third consecutive defeat
Bednarek gave Southampton the lead a minute before half-time after the Saints 'keeper had brilliantly denied Bukayo Saka from scoring early on
The 34-year-old then made a string of fine saves in the second half, with Arsenal striker Alexandre Lacazette missing after testing positive for Covid, to give the hosts their first victory in six matches
Gabriel Martinelli forced the first save from Forster in the ninth minute when he cut in from the right and sent a bending shot towards the far corner which the goalkeeper parried away
But Forster's best stop - and perhaps of the season - came from a Southampton mistake inside their own half
 Yan Valery telegraphed his pass into Lyanco allowing Eddie Nketiah to intercept and he moved the ball out to Martinelli, who crossed for Saka but his close-range effort was wonderfully pushed behind by the right hand of Forster
Nuno Tavares returned to the Arsenal team at left-back for the first time since he was hauled off at half-time against Crystal Palace earlier this month
 He had a solid 70 minutes and drew two fouls in the Southampton final third during the first half, the second resulting in Cedric Soares firing the set piece over when crossing into the box was the better option
Arsenal dominated possession with Southampton unable to launch any meaningful counter-attacks in their new-look 3-4-3 formation, but they grabbed the opener a minute before half-time through an unlikely source
 Arsenal cleared James Ward-Prowse's corner but then switched off when it was recycled into the area by Romain Perraud
 Mohamed Elyounoussi turned the ball back for Bednarek, who finished coolly first time as Ramsdale got a hand to it but could not keep it out
Arsenal have won just four points from losing positions this season - only Wolves (3) have taken fewer - and at the start of the second half it was clear the trend was set to continue
 Perraud was denied making it two by an excellent block from Ben White after burrowing his way into the area
Emile Smith Rowe's introduction on the hour was much-needed for Arsenal with the midfielder instantly breaking onto a loose ball in the Southampton area but saw his shot blocked by Martinelli
Then Smith Rowe was brilliantly denied by Forster as the Southampton 'keeper clawed away his close-range volley before he saved again from Saka which led to Martin Odegaard firing the follow-up wide
 There was still time for Forster to push away a curling effort from Granit Xhaka late on
Arsenal manager : "It is difficult to explain because this is football, not basketball
 In any other sport you win the game very comfortably
"At the end of the day it's decided in the boxes, they scored one goal, we didn't for that amount of time we spent around the box, the clear-cut chances we had, we didn't put them in the goal because they have an exceptional goal have an exceptional goalkeeper today, and because we didn't have enough quality to break them down
"Asked whether Arsenal's top-four challenge is losing impetus, he said: "It certainly has and we need to find a way to win football matches
 What we can do is play as good as possible to get the team as close as possible to win football matches - today we've done that again
 The stats will say, 'How the hell have we lost that game?' but the reality is we lost it
"A relieved  was delighted his side could break their six-game winless streak to emerge victors over faltering Arsenal, who failed to score despite registering 23 attempts on goal
Saints delivered an uncharacteristic display in the wake of last week's 6-0 mauling by Chelsea - opting to concentrate on defensive resilience in favour of their usual pressing style
"We knew that it was time to show a reaction," the Austrian said
 "And to show that we also can play a little bit different
 Today was a different game; under 30 per cent possession I don't think we've ever had in this season so far
 We didn't want to give them a chance for an early ball in
 We wanted to be compact
"We wanted to minimise the mistakes we've made in recent weeks because you have to when you concede 13 goals in four games
 You have to change things
 This is what we did today
 I know that we can play more football, I know that we can play better
 But it's also good to know that we can defend like this
"He reserved a word of praise for the performance of Forster, who is out of contract at the end of this season, but proved invaluable against Arsenal's armoury: "A goalkeeper who was exceptional today
 Not to forget, because otherwise, it looks different
"Great to get such a reward for such a game
 This is absolutely exceptional
 I'm very happy for him
 He plays for winning with Southampton and definitely for staying with us
"Arsenal travel to Chelsea on Wednesday at 7
45pm - live on  - before Southampton head to Burnley on Thursday at 7
45pm - live on April 20 - , April 23 - May 1 - , May 8 - , May 12 - , May 16 - May 22 - 
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>
<PAD>