The match marked the return of Gunners great Thierry Henry who emerged as a second-half sub to score his 227th goal for the club (and 12th in 12 against Leeds) with just over 10 minutes remaining to send the North Londoners through to the next round where they will meet Premier League rivals Aston Villa at home.
It was a rather undistinguished encounter with neither side really dazzling in their play and it took a 34-year old in Henry to break the deadlock with a customary cool finish.
In the 78th minute, just ten minutes after coming on, the New York Red Bulls man received a deft ball from Alex Song on the left side of the area to take a neat first touch before sliding a clinical finish past Andy Lonergan to the far post which sent the Arsenal faithful into raptures.
Arsenal goalkeeper Wojciech Szczesny's goal was never really threatened except for when Luciano Becchio blasted over from close range in the 24th minute and veteran Michael Brown hit a crisp strike which was safely-held by the Pole in the 79th minute before he was tested late when Mikael Forssell struck on the turn.
Down the other end, Lonergan was by far the busiest of the two keepers although Arsene Wenger's men were wasteful with Alex Oxlade-Chamberlain, Mikel Arteta and Aaron Ramsey controlling proceedings but being unable to breach an inexperienced Leeds defence which held their own for almost the entirety.
Nonetheless, it was Arsenal's night as a punt on a returning hero's class and composure paid immediate dividends on the first appearance of a potentially successful and eventful two-month loan agreement.
FA Cup third round
Emirates Stadium, London