Southampton's winless start to the season continued as a late Santi Cazorla penalty gave Arsenal all three points in a 2-1 loss in the capital, leaving Claude Puel’s men in the relegation zone.
The Saints took the lead through Petr Cech's own goal after Dusan Tadic's freekick deflected off the bar and onto Cech's back, but the home side levelled through birthday boy Laurent Koscielny's overhead kick and won the game with Cazorla's late spot-kick in injury time.
Ryan Bertrand made his long-awaited first start of the season after the left-back had recovered from injury, whilst Puel’s opposite number Arsene Wenger gave debuts to £55m newboys Lucas Perez and Shkodran Mustafi.
On a wet afternoon at the Emirates, it took a while for the game to get going but Saints made the perfect start to the game after quarter of an hour. Tadic’s 25-yard free kick swerved onto the crossbar and rolled in off the back of the hapless Cech to give Southampton an unlikely, but deserved, lead.
Arsenal went close to equalising ten minutes later as Walcott met Cazorla’s freekick, but the former Saint’s header flew harmlessly over the bar. Five minutes later though, the home side drew level on the half hour. A flick-on from a corner found its way to the free Koscielny, and the Frenchman acrobatically volleyed home with his back to goal.
Whilst the game sauntered to half-time with Arsenal now on top, the interval did bring a surprise as Shane Long came on for Jay Rodriguez as Puel persisted with the diamond formation. The change did not stop Arsenal coming back into the game far more than in the opening stages, with Forster's booking typical of the Saints' cautious approach; a confusing switch after success by playing on the front foot in the first half hour.
Arsenal could smell blood and the introduction of Alexis Sanchez and Olivier Giroud, a regular goalscorer against the Saints in recent years, suggested that they were looking to take full advantage.
Long had a golden chance to regain the lead when Tadic played the substitute in behind the Arsenal defence, but the Irishman screwed his shot wide with the goal at his mercy. The striker was almost punished straight away for his profligacy, but the Gunners' own number 7 Alexis put his effort over the bar from 12 yards after finding time and space.
Saints' had chances to retake the lead, with Long nodding a header over the bar from a good Redmond cross, but their lack of ruthlessness meant that Arsenal looked dangerous from every attack. A rare Van Dijk error could have been punished shortly after, but Cazorla's shot flew narrowly wide in a nervy period for the away side.
Long's poor day in front of goal after stepping off the bench was summed up with just seven minutes left as the Irishman was first to Cech's rebound following Hojbjerg's effort from range, but the striker scuffed his shot and the ball harmlessly rolled into the Arsenal keeper's hands. At the opposite end, Giroud nodded a header just wide as the clock ticked towards full time.
But deep into injury time under late pressure from the home side, Southampton conceded a penalty. After a clearance was sweeped back in, Jose Fonte was penalised for a trip on Olivier Giroud. Santi Cazorla stepped up and coolly dispatched the spot-kick in the dying minutes to win Arsenal the game in a somewhat cruel loss for the Saints.
Arsenal: Cech; Bellerin, Mustafi, Koscielny, Monreal; Coquelin, Cazorla; Walcott, Ozil, Oxlade-Chamberlain (Alexis 61'); Perez (Giroud 61').
Subs not used: Ospina, Holding, Elneny, Xhaka, Iwobi.
Booked: Monreal 17’ Cazorla 26'
Southampton: Forster; Cedric, Fonte (c), Van Dijk, Bertrand; Davis, Clasie (Hojbjerg 65'), Romeu; Tadic (Ward-Prowse 80'); Redmond, Rodriguez (Long 45').
Subs not used: McCarthy, Yoshida, Austin, Targett.
Booked: Forster 54', Pierre-Emil Hojbjerg 86' Virgil van Dijk 90' Ryan Bertrand 90' Jose Fonte 90'
Referee: Bobby Madley