London - Arsenal extended their lead at the top of the Premier League to four points after Olivier Giroud capitalised on a shocking mistake by Southampton goalkeeper Artur Boruc to set his side on course for a 2-0 win at the Emirates Stadium on Saturday.
Giroud wrapped up the victory with an 86th minute penalty - his seventh league goal of the season - to ensure Arsene Wenger's side took full advantage of second-placed Liverpool's failure to beat Everton in the Merseyside derby earlier in the day.
France forward Giroud had given Arsenal a 22nd minute lead when Boruc was caught in possession with the ball at his feet.
Giroud's goals condemned Southampton to only their second league defeat of the season and snuffed out any hope Mauricio Pochettino's side had of claiming the win that would have moved them to the top of the table.
Southampton arrived in north London boasting the best defensive record in the Premier League after conceding just five goals in their opening 11 games, one fewer than Tottenham Hotspur.
The last thing Arsenal expected, then, was to be gifted an opening goal by the kind of lapse that will give Boruc nightmares.
Poland international Boruc inexplicably failed to clear his lines after collecting a back-pass from Nathaniel Clyne and allowed Giroud to close him down before attempting to round the striker with a series of clumsy drag-backs.
Giroud eventually poked the ball away after the keeper had twisted and turned three times and, with Boruc stranded, rolled the ball into an unguarded net.
Earlier this month Boruc had been beaten by a long clearance by Stoke keeper Asmir Begovic but this was more embarrassing even than that misjudgement.
As unfortunate as the 22nd minute goal was for the visitors, they had enjoyed two slices of good fortune earlier in the game as Arsenal responded well to a positive opening from the south coast side.
Jack Wilshere, operating in an unfamiliar position on the right, moved into the penalty area to collect a flick from Giroud and clipped a right foot chip from a tight angle that rebounded to safety off the inside of the far post in the ninth minute.
Then, nine minutes later, Aaron Ramsey showed he is a player full of confidence at the moment when he connected with Mesut Ozil's cross with a back heel flick from 12 yards out only to see his effort strike the woodwork with Boruc beaten.
Southampton's reaction to falling behind would provide a measure of their progress this season and they responded positively with their trio of new England internationals - Adam Lallana, Rickie Lambert and Jay Rodriguez - leading the way.
Lallana tested Arsenal keeper Wojciech Szczesny with a dipping volley from the edge of the area that the Pole did well to tip to safety.
And the keeper produced an even better save to deny Rodriguez's acrobatic shot with Lambert's follow-up flashing across the face of goal.
Southampton maintained their momentum after the re-start with Lallana again testing Szczesny with an excellent left foot shot following a sweeping counter-attack.
But Arsenal exerted more control the longer the game went on as they went in search of the second goal that would ensure they avoided an uncomfortable end to the game.
And the feelgood factor around the stadium was enhanced by the return of England winger Theo Walcott as a 74th minute substitute after a two month absence following abdominal surgery.
The second goal eventually came four minutes from time when Per Mertesacker was held by Jose Fonte at a corner and Giroud scored with a left-footed shot from the ensuing penalty.