United manager Simon Grayson made two enforced changes his starting line-up from the one which crushed Scunthorpe 4-0 at the weekend. ben Parker came in for the inelligible George McCartney and Billy Paynter was handed his second Elland Road start in place of the injured Luciano Becchio.
The atmosphere was electric with over 38,000 inside the ground, and Leeds rose to the occasion by looking to make the early running. Max Gradel had a shot wide and Jonny Howson threatened early.
But, in typical Arsenal fashion, the visitors stole the lead inside five minutes with their very first attack. Keiran Gibbs was involved and Samir Nasri finished off a flowing move with a drifting run and a great strike to leave Kasper Schmeichel with no chance.
Five minutes later, Schmeichel was called upon to make a superb save to claw away a Maroume Chamakh header from a corner.
Arsenal were quite simply outstanding at times during the opening 20 minutes when in possession, and Leeds looked to play on the break. Schmeichel saved well from Nicklas Bendtner, and Leeds looked to the inventiveness of Jonny Howson and the pace of Max Gradel and Sanchez Watt.
But it was the Gunners who carved out another chance on 27 minutes when Bendtner came within a whisker of converting a low cross.
Robert Snodgrass forced Wojciech Szczesny into making his first save of the night on the half-hour, but the visitors went straight down the other end of the field and doubled their advantage. This time it was Bacary Sagna who finished off the move with a stunning strike.
But Leeds were back in it within three minutes. A Gradel cross was half-cleared, Howson teed up Bradley Johnson and the midfielder scored with a stunning strike from distance.
It was a superb goal, and the final 10 minutes of the first half saw some competitiveness from both sides with Leeds having a foothold back in the game.
The Gunners started the second half on the offensive, though, and Schmeichel had to save well twice inside the opening three minutes.
But United were more than competing in the contest, and when Arsenal threatened again Snodgrass made a brilliant tackle to deny a certain goalscoring opportunity.
When United came forward with a good passing move, Sagna made a decisive challenge to thwart Watt. Shortly after the hour, Gradel escaped down the right and Paynter came within a whisker of turning his cross goalwards.
With 25 minutes left, Grayson had to make his first change of the game when Andy O'Brien limped off to be replaced by Leight Bromby. Moments later, Davide Somma was introduced in place of Paynter, and his first touch was to divert a cross just wide of the mark.
The Gunners also made two changes on 71 minutes, Cesc Fabregas and Robin Van Persie joining the fray. And the duo both had an immediate impact.
Fabregas released Bendtner down the right and the Scandinavian swung over a perfect cross which Van Persie rose superbly well to head home.
That proved the deciding factor in the contest, despite a gallnt finish from Leeds, it was Arsenal who progressed through to the fourth round.