By Chris Harris at St. Mary's
Arsenal missed their chance to go top of the Premier League after slipping to a heavy defeat at Southampton.
Cuco Martina's world-class strike left the Gunners with an uphill task, Shane Long tucked in a second early in the second half and Jose Fonte's header effectively ended the Gunners' hopes.
The visitors were aggrieved - Long appeared to trip Laurent Koscielny in the build-up to his goal - but they couldn't find a response against a spirited Saints side. And Long rubbed salt in their wounds with a fourth in stoppage time.
Olivier Giroud and Theo Walcott went close with first-half headers but Arsenal lacked their usual sharpness and struggled to create chances in open play.
No side has won as many points as the Gunners have in 2015 and, as Arsene Wenger said ahead of this game, his team is still "on the right train, heading the right way".
But such is the nature of the Premier League - and this season in particular - that any drop in performance is ruthlessly punished.
There is a small consolation: Arsenal only have to wait 48 hours for a chance to get back on track - against Bournemouth at the Emirates.
SETTING THE SCENE
Arsenal arrived at St. Mary's for their Boxing Day assignment with the perfect incentive - a win would take them top after Leicester came a cropper at Liverpool earlier in the day.
The form book favoured the Gunners. They went into the game on a three-match winning streak; Southampton hadn't won in six. But Arsenal have struggled on the south coast in recent years, victorious on just one of their last six visits.
Wenger stuck with the side that beat Manchester City on Monday, naming one former Saint in his starting line-up - Walcott - and two more on the bench - Alex Oxlade-Chamberlain and Calum Chambers.
On his 25th birthday, Aaron Ramsey continued his midfield partnership with Mathieu Flamini, and Giroud was looking to score in five consecutive games for the first time in his career.
Arsenal had a golden opportunity to break the deadlock inside two minutes.
Ozil - already the proud owner of 15 assists this season - was denied a 16th when Giroud sent a free header over the bar from a corner. There were mitigating circumstances - a blustery wind that affected dead balls throughout the game - but Giroud usually snaffles those chances.
An Ozil free-kick drifted just beyond Per Mertesacker as Arsenal continued to start brightly but Southampton's energetic pressing soon told.
Sadio Mane, Steven Davis and James Ward-Prowse grew into the game and, with Long running the channels eagerly, the home side pushed Arsenal back, denying Ramsey and Flamini time on the ball.
Ryan Bertrand's marauding run ended with a timely intervention from Mertesacker but no one could do a thing about Martina's stunner in the 19th minute. Mertesacker cleared as far as the 26-year-old and he buried a first-time shot beyond Petr Cech from 30 yards.
It really was an incredible strike - the trajectory of Martina's shot had shades of Roberto Carlos's famous free-kick for Brazil against France - and it left Arsenal facing an even stiffer task.
Nacho Monreal was a regular outlet on the left and he forced a save from Maarten Stekelenburg after Giroud's header from Ozil's cross was blocked. But in general Arsenal struggled to create in open play as Saints players snapped at their heels.
Walcott flicked a header just wide of the near post from another accurate Ozil corner but Long had an even better chance when he ran onto Mane's clipped pass - only to fire well over Cech's crossbar.
Virgil van Dijk had the ball in the net a few minutes after the restart but his header was ruled out for a marginal offside.
Arsenal weren't so lucky when Long and Mane burst forward on the counter-attack.
Long found Mane and appeared to clip Koscielny as the two crossed paths on their way to the penalty area. Koscielny went down, Long was suddenly free in the box and Mane squared the ball for his team-mate to tap in.
The visitors complained but to no avail, and the onus was now on them to find a way back into the match.
Ramsey tried his luck from the edge of the box but a deflection took the edge off his shot. Then Wenger brought on Oxlade-Chamberlain but Arsenal were rocked again when Fonte rose to power a header past Cech from Bertrand's corner.
Dusan Tadic's snap-shot forced an acrobatic save from Cech and Ozil saw an effort roll along the goal-line after good work from substitute Alex Iwobi.
Arsenal were briefly spared a fourth goal when Long got clear of Mertesacker to slide a shot against the post. But the Saints striker had the final word with a low finish in stoppage time.
Referee: Jonathan Moss
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