Theo Walcott came off the bench to net a late winner and send Arsenal into the fifth round of the FA Cup with a thrilling 3-2 victory at Brighton.
In-form Olivier Giroud fired the visitors ahead on 16 minutes before Ashley Barnes equalised with a powerful header. Giroud netted again on 56 minutes with another well-taken strike, but the Seagulls were level again through a diving header from Argentinian forward Leonardo Ulloa on his debut after joining from Almeria.
Arsenal finally made sure of a place in the last 16, though, when Walcott's shot was deflected in following a corner with five minutes left.
Brighton, hoping to add to their third-round scalp of Newcastle here, started brightly. On 15 minutes a floated a ball in from the left over a static Arsenal defence saw Barnes clear on goal with no offside flag. However, Wojciech Szczesny was quickly off his line to narrow the angle and made a superb reaction save to push the ball past the post.
It proved decisive as Arsenal went up the other end and opened the scoring. Lukas Podolski was the provider, creating space on the edge of the penalty area before feeding Giroud, who curled the ball into the bottom left corner for a third goal of the week.
Brighton, though, refused to lie down and were level on 33 minutes. A short corner was whipped in from the right, and Barnes charged through a sea of red shirts to get to the ball before Szczesny and power a header into the back of the net.
Arsenal were back in front on 56 minutes with another brilliant finish from Giroud. Diaby floated an angled pass into the left side of the penalty area, where Frenchman Giroud held off Adam El-Abd, took the sting out of the ball with a lovely first touch and then lashed it into the net from six yards.
Brighton, though, refused to lie down and were back on level terms after 62 minutes. Arsenal again failed to deal with a cross from the right as Barnes' ball in was dispatched past Szczesny with a diving header by Ulloa.
With 20 minutes left, Wenger sent on Walcott and Jack Wilshere, replacing Rosicky and Oxlade-Chamberlain. Podolski got away down the left and cut the ball back for Giroud, but this time the France striker could only hack a half-volley wide.
An acrobatic effort from the Arsenal number 12 was then put behind, and from the resulting corner Walcott won it when his shot was deflected off El-Abd and into the net to send the Gunners through to the fifth-round draw.