Arsene Wenger's men overturned a 4-0 deficit to enjoy the spoils, and more importantly, progress into the competition's quarter-final round.
Plenty of youngsters had the opportunity to shine in this match. How did they perform? Let's take a look.
Damian Martinez: 4/10
Martinez will be bitterly disappointed with his performance.
He was lucky to escape an early chance where the ball cannoned off the post and onto his head. Martinez did well to smother an opportunity for Jay Tabb, but then misjudged the resulting corner.
His attempt at stopping Reading's third goal was laughable. The 20-year-old then made a decent save before eventually getting beaten by an excellent Noel Hunt header.
Extra time was also a mixed bag. Martinez got behind a Jobi McAnuff attempt when the game restarted. He was then booked for time wasting and distributed the ball straight to the opposition in vital moments.
Ignasi Miquel: 6/10
Started with composure. Cleared a couple of testing crosses and took up decent positions early on. Quickly became ragged and didn't get close enough to the opposition in the build-up to Reading's second goal.
Received a yellow card for a slightly late challenge on the half hour mark. Didn't work so doggedly after his booking, but put in a decent shift. Was fortunate not to concede an own goal early in the second half.
Subbed off 17 minutes into extra time.
Carl Jenkinson: 8/10
An assured performance from the first team regular. Happy to support Arshavin in attack and provided a great cross which Theo Walcott stubbed just wide.
Really came to the fore in the second half. Got forward with great pace and ensured the team had width. Jenkinson confirmed extra time by following Walcott's effort with a brilliant finish.
Francis Coquelin: 9/10
The Frenchman was one of Arsenal's star performers.
Took control of the midfield shortly before the break. Settled into the game with controlled touches and increased tenacity. He looked to bring his colleagues into the match by spreading play across the pitch.
Coquelin's energy was also rather impressive. He continued working for 120 minutes without ever looking off the pace. Will give Arsene Wenger something to think about in the next few weeks.
Emmanuel Frimpong: 5/10
Looked unfit in a fast-paced match. Particularly sloppy in the first 20 minutes. Movement seemed slow, especially alongside Coquelin. Played some decent passes but became rattled after conceding the fourth goal.
A useful hour for the youngster's fitness. Was rightfully sacrificed on 62 minutes.
Serge Gnabry: 5/10
Fed on scraps in the first half. Was confident on the ball but played a couple of sloppy passes from decent positions.
Forced Mikel Leigertwood into a poor effort with a decent slide. Saw more of the play in the second half, where he turned on the pace and showed some skill. Gnabry's best effort came with a shot that landed just wide of Adam Federici's post.
Subbed on 62 minutes. His replacement, Mr Olivier Giroud, made an instant impact by scoring Arsenal's second.
Thomas Eisfeld: 7/10
Entered the game in the 62nd minute and looked really sharp. Had a style and intelligence about his play. Took up some great positions between Reading's two rows of four. Fluffed an attempt from long range when better options were available. Provided Giroud with an accurate cross, resulting in a fine save from Federici.
Booked for a cynical foul just after Arsenal conceded the fifth.
Jernade Meade: N/A
Replaced an injured Miquel with 13 minutes of extra time left. A couple of decent touches, although played a terrible ball with three minutes to go. Didn't have time to make much of an impression.
How did you rate the performances of Arsenal's youngsters? Let me know in the comments section below, and be sure to follow me on Twitter: Follow @Nakerman