Arsenal kept pace with Manchester City at the top of the Premier League table after going up a gear in the second-half to win 3-0 at Swansea.
The Gunners were second-best in the first period but had a couple of narrow escapes and then took the lead through Oliver Giroud just after half-time.
And the decisive moment of the match came in the 68th minute when Laurent Koscielny turned the ball into a gaping net and the goal was allowed to stand, although the Swansea players were convinced goalkeeper Lukasz Fabianski had been fouled.
Joel Campbell then capped a great day for Arsenal four minutes later, lashing the ball into the net to score his first goal for the club, on the day he made his first Premier League start.
Alex Oxlade-Chamberlain and Theo Walcott were unavailable to the visitors after picking up injuries in midweek, joining a lengthy list of absentees which may hinder the Gunners in the weeks ahead.
And a 3-0 away win looked an unlikely scenario in the first-half as Arsenal struggled to contain a lively Swansea side who did the double over them last season.
The Swans should have taken the lead just after the 20-minute mark when Jonjo Shelvey's fine pass put Bafetimbi Gomis clean through on goal.
However, the forward is struggling for goals at the moment and delayed his shot too long, taking the time to go round Petr Cech but giving Hector Bellerin time to get back and produce a brilliant goal-saving tackle.
With Jefferson Montero a constant threat down the left, the Swans continued to press and they had a strong case for a penalty when the winger won a free-kick on the edge of the box and Per Mertesacker appeared to block Gylfi Sigurdsson's shot with his arm, unseen by the officials.
Arsenal created one decent first-half opportunity but Giroud put his first-time shot over the crossbar after he had been played in by Alexis Sanchez.
However, the French forward made no mistake two minutes into the second-half, eluding his marker Ashley Williams at a Mesut Ozil corner in expert fashion and then nodding the ball into the net from close range to score Arsenal's 2,000th goal under Arsene Wenger's management.
Swansea were far from dispirited by the setback and stormed forward with renewed hunger, Sigurdsson drawing a great save from Cech with a piledriver from the edge of the box.
And Bellerin then produced an incredible block to deny Andre Ayew, the fact the flag had gone up for offside not detracting from the defender's bravery, as he crashed into a post in order to keep the ball out.
The Swans then had the stuffing knocked out them by a bizarre second goal, which came when Ozil crossed and the ball looped into the air off Williams, allowing Giroud and Koscielny to challenge Fabianski.
The former Arsenal man dropped the ball under pressure but no free-kick was given and Koscielny was able to tap the ball into the net and double the visitors' advantage.
A third goal soon followed and it was far more typical of the Gunners, Ozil exchanging passes neatly with Sanchez and then sending over a low cross from the left which Campbell finished off superbly at the back post, taking a touch before drilling the ball emphatically into the far corner.
Swansea remained defiant and Williams drew another good save from Cech, but the game was now set up perfectly for Arsenal and it was somewhat surprising that they did not add further goals as they charged forward on the break in the closing stages.
However, three were more than enough for the travelling contingent, as what had looked like being a really tough afternoon turned into a comfortable win, and three vital points which keep the Londoners in the thick of the title race.
Soccer Saturday Verdict - Phil Thompson
"Arsenal were very poor in the first half by their own standards. Their passing was sloppy and the concentration from the players was not there.
"At half-time they were probably happy to go in at 0-0, because they got away with a penalty decision when Gylfi Sigurdsson's free-kick hit Per Mertesacker's arm.
"Bafetembi Gomis has a wonderful opportunity. What a ball by Jonjo Shelvey to split the defence and Gomis is away. He has a clear run through but Petr Cech stays big and strong and forces him away from goal.
"At the time I thought Swansea could rue that chance and that's exactly what happened."
Swansea: Fabianski (5), Taylor (6), Williams (6), Naughton (6), Fernandez (6), Ki (6), Shelvey (7), Ayew (6), Montero (7), Sigurdsson (6), Gomis (5)
Substitutes: Britton (6), Eder (6), Barrow (6)
Arsenal: Cech (8), Mertesacker (6), Koscielny (7), Monreal (6), Bellerin (8), Ozil (6), Sanchez (6), Cazorla (6), Campbell (7), Coquelin (6), Giroud (7)
Substitutes: Gibbs (6), Chambers (6), Iwobi (6)
Star Man: Hector Bellerin