Arsenal missed the chance to go top of the Premier League as Arsene Wenger's men were soundly beaten 4-0 by a much-improved Southampton at St Mary's Stadium on Saturday.
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Wenger's side fuelled talk of a sustained title push with an impressive victory over Manchester City on Monday, but were punished for a lethargic display on the south coast as the hosts ended their run of five league games without a win in style.
Southampton had picked up just a point from their previous five outings, but, after a slow start, went ahead courtesy of Cuco Martina's impressive long-range effort 19 minutes in.
On his maiden Premier League start, Martina became the first Curacaoan to score in the division and Southampton grew in confidence, doubling the lead 10 minutes into the second half via the first of a Shane Long brace.
With limited attacking options on the bench, Wenger saw his side toil in the final third and struggle defensively as they failed to leapfrog leaders Leicester City - beaten 1-0 by Liverpool earlier in the day and two points clear of Arsenal.
Instead, Southampton - missing the likes of injured pair Graziano Pelle and Cedric Soares - saw Jose Fonte head in a third from a corner and Long make it 4-0 in stoppage time shortly after being denied by the woodwork to seal the points on a hugely frustrating evening for the visitors.
An unchanged Arsenal edged the opening stages, but fell behind to the hosts' first effort on target.
Per Mertesacker only partially cleared Ryan Bertrand's delivery, allowing Martina to beat Petr Cech with a stunning outside-of-the-boot effort.
James Ward-Prowse dragged a shot wide before the half-hour mark as the home side grew in confidence, with Steven Davis failing to muster a clean strike on goal after Laurent Koscielny lost possession.
For all their early endeavour, Arsenal's best chances were a tame Theo Walcott shot easily gathered by Maarten Stekelenburg and a header from the Arsenal winger that found the side-netting.
Long almost doubled Southampton's half-time lead, but the striker could only put his lob over the crossbar while Sadio Mane's dangerous delivery failed to get the necessary touch early on the second half.
Virgil van Dijk had the ball in the net five minutes after the interval - his header adjudged offside - although Long did make it 2-0 with a breakaway goal before the hour.
The Republic of Ireland international played a neat one-two with Mane, before turning his team-mate's cross past Cech from close range amid Arsenal complaints over a perceived trip from Long on Koscielny.
Arsenal continued to flounder going forward, with the likes of Mesut Ozil and Joel Campbell largely anonymous in the face of incessant Saints pressure.
Former Southampton man Alex Oxlade-Chamberlain was introduced for the latter after the hour, but it was Southampton who remained the more clinical, skipper Fonte heading home from Bertrand's set-piece 21 minutes from time.
The impressive Long hit the post, but was not to be denied a second when Dusan Tadic set him clear, the Saints forward finishing past Cech to complete a miserable outing for Wenger's men.
Key Opta stats:
- Arsenal have lost two successive league meetings with Southampton for the first time since April 1988.
- Cuco Martina was the first player from Curacao to score a Premier League goal - 93 different nationalities have now scored in the competition.
- Arsenal have conceded five Premier League goals from outside the box in 2015-16 so far; two more than in the whole of 2014-15 (3).
- Sadio Mane has six assists in 18 Premier League appearances this season; twice as many as he had in 30 Premier League last season (3).