Playing at home for a fifth successive outing, Arsene Wenger's side eventually prevailed in a see-saw contest to record their 150th league victory at the Emirates Stadium.
Welbeck was the hero for the hosts, the forward on hand at the back post to nod home Alex Iwobi’s deep cross for the winner just moments after he had failed to convert a glaring opportunity inside the six-yard box.
The England international had found the net in the first half too, his deflected drive making it 2-1 after Pierre-Emerick Aubameyang’s poked finish had cancelled out Shane Long’s early opener for the visitors.
Substitute Charlie Austin appeared to have grabbed a point when he scored within two minutes of his introduction, the striker on hand to turn home Cedric’s cross, but the Saints could not hold on and they remain in the drop zone, three points adrift of safety.
Jack Stephens saw red for shoving Jack Wilshere in the face in an eventful conclusion, while Arsenal also finished the game down to 10 after Mohamed Elneny’s dismissal for violent conduct in the aftermath.
Defeat was tough on Southampton, who had seen Hector Bellerin clear James Ward-Prowse’s goal-bound effort off the line before they caught their hosts sleeping at the back to take the lead.
Cedric’s cross appeared easy for Arsenal to deal with, yet a mix-up between Shkodran Mustafi and Petr Cech allowed the alert Long to squeeze ahead of the former and stab the ball in from close range.
Yet the opening goal only served to kick-start Wenger’s side out of their slumbering state.
Welbeck’s clever touch presented Aubameyang with the chance to prod the ball beyond the advancing Alex McCarthy for his sixth league goal of the campaign and, after setting up the equaliser, the former fired his side ahead with a right-footed drive that clipped defender Maya Yoshida's leg.
7 - Pierre-Emerick Aubameyang has been directly involved in seven goals in the Premier League this season (six goals, one assist); the most of any Arsenal player in their first seven appearances in the competition. Gunner. pic.twitter.com/NxpgviwTVy— OptaJoe (@OptaJoe) April 8, 2018
McCarthy had little chance with the goal but did at least keep the gap at one in the early stages of the second half, turning away shots from Aubameyang and Granit Xhaka in quick succession, though it was far from one-way traffic.
Cech repelled firm drives from Pierre-Emile Hojbjerg and Wesley Hoedt but required assistance from Elneny to keep out a header from Stephens, the Egyptian midfielder - stationed on the back post for a corner - nodding the ball clear with his keeper beaten.
Long saw a potential equaliser chalked off for offside before Austin’s immediate impact off the bench, the striker’s close-range finish raising Southampton’s hopes of picking up at least a point in their fight for survival.
Yet they will return to the south coast with nothing to show for their efforts, Welbeck heading in the game’s decisive fifth goal before tensions boiled over during added time.
Stephens was shown a straight red by referee Andre Marriner for reacting to Wilshere’s jersey pull, with Elneny quickly following the Southampton defender down the tunnel after raising his hands to Cedric.
Key Opta stats:
- Arsenal have won six matches in a row in all competitions for the first time since May 2017 (also six).
- The Gunners have scored 3+ goals in five successive home games in all competitions for the first time since their opening six matches of the 1958/59 season.
- Southampton have lost three successive away league matches conceding at least three goals in each for the first time since September 2013, under Nigel Adkins (a run of four).
- Southampton haven’t won any of their last six Premier League games in which they have opened the scoring (D4 L2).
- Mark Hughes has now lost each of his 11 trips to Arsenal in the Premier League, only Harry Redknapp against Manchester United (15) is on a longer wait for an away win against an opponent in the competition.
- Danny Welbeck both scored and assisted in a Premier League match for the first time since September (v Bournemouth), which was also the last time he netted a league goal.
- Shane Long has scored four goals against Arsenal in the Premier League, only against Aston Villa (6) has the Irishman netted more often.
- In fact, only Wayne Rooney (7) and Robin Van Persie (6) have scored more Premier League goals against Petr Cech than Shane Long (5).
- Charlie Austin has scored in each of his four Premier League games against Arsenal (four goals), including in both of his appearances at the Emirates.