London: A calamitous mistake by Southampton goalkeeper Artur Boruc set Arsenal en route to a 2-0 victory that sent the Premier League leaders four points clear on Saturday.
Arsenal had already hit the woodwork through Jack Wilshere and Aaron Ramsey at the Emirates Stadium when Boruc attempted to outwit Olivier Giroud with some fancy footwork inside his penalty area in the 22nd minute.
The Poland international attempted one drag-back too many, however, enabling Giroud to steal possession and stab home the opening goal.
Giroud made sure of victory with four minutes remaining, registering his 10th goal of the season from the penalty spot after Jose Fonte had been penalised for pulling Per Mertesacker`s shirt.
"I`m very happy because we were against a good team and they showed why they made good results before," said Arsenal manager Arsene Wenger, whose side are only the second team to beat Southampton in the league this term.
"We couldn`t take our chances, but we took advantage of their mistakes. It`s a very good win against a difficult team.
"They are a good team and if they had won today they would have been level with us at the top of the league, so that shows you how good they are."
Victory left Arsenal four points above second-place Liverpool, while Chelsea leapfrogged Southampton to third place -- level on points with Liverpool -- after winning 3-0 at West Ham United in the day`s late game.
Frank Lampard opened the scoring against his former club with a 21st-minute penalty after Jussi Jaaskelainen sent Oscar tumbling, and Oscar then made it 2-0 with a low drive.
West Ham manager Sam Allardyce reacted by sending on Mohamed Diame and Modibo Maiga before half-time, but although the hosts exerted more pressure on the Chelsea penalty area, Lampard made the game safe in the 82nd minute when he swept home from 18 yards.
Earlier, Daniel Sturridge came off the bench to earn Liverpool a 3-3 draw against Everton with an 89th-minute equaliser in a frenetic and richly entertaining Merseyside derby at Goodison Park.
A brace from Romelu Lukaku had put Everton on the brink of a first win over their city rivals in seven matches, but Sturridge`s header gave Liverpool a share of the spoils after a breathless encounter.
"It was a terrific game. I`ve been involved in a few and they are real heart-stoppers," said Liverpool manager Brendan Rodgers.
"We again showed our resilience and ability to fight back. This is a difficult place to come and they haven`t lost at Goodison Park this year."
Philippe Coutinho`s fifth-minute opener for Liverpool was swiftly cancelled out by Kevin Mirallas, before Luis Suarez restored the visitors` lead in the 19th minute by bending a 25-yard free-kick into the bottom-right corner.
Mirallas was fortunate to avoid a red card for a knee-high foul on Suarez before half-time, but he teed up Lukaku for both the equaliser and the 82nd-minute header that put Everton in front.
Everton would have moved level on points with Liverpool if they had won, but Sturridge had the final say when he smartly headed past goalkeeper Tim Howard from a Gerrard free-kick.
Everton manager Roberto Martinez said: "It`s really disappointing we didn`t get three points. To concede late on from a dead-ball situation doesn`t reward my team for how they played in the second half."
Freshly-appointed Crystal Palace manager Tony Pulis watched from the stands as his new side overcame the dismissal of Yannick Bolasie to win 1-0 at Hull City.
Bolasie was sent off for a clumsy challenge on Jake Livermore in the 78th minute, but Barry Bannan scored from a Cameron Jerome cut-back three minutes later to give Palace a first away win of the campaign.
Victory at the KC Stadium took Palace off the foot of the table at the expense of Sunderland, who went down 2-0 at Stoke City.
Charlie Adam and Steven Nzoni scored in either half for Stoke, while Wes Brown was sent off for a seemingly clean challenge on Adam in the 36th minute, provoking a furious reaction from Sunderland manager Gustavo Poyet.
Fulham remain in the bottom three after losing 2-1 at home to Swansea City, while Newcastle United closed to within two points of the Champions League places after winning 2-1 at home to Norwich City.