Arsenal came from 4-0 down to beat Reading in extra time and advance to the fifth round of the Capital One Cup this evening in a 12-goal blockbuster at the Madejski.

The hosts raced into their four-goal lead after just 38 minutes before late drama saw the Gunners send it into a further 30 minutes, where Theo Walcott completed a hat-trick.

Early on Sean Morrison headed against the frame of the goal before Jason Roberts gave the Royals the lead in the 12th minute by volleying Hal Robson-Kanu's cross into the roof of the net.

It was soon two and then three as first Laurent Koscielny diverted Chris Gunter's centre into his own net before young Gunners keeper Damian Martinez palmed Mikele Leigertwood's shot behind him into the goal.

Reading were were remarkably four up when Gareth McClearly clipped a cross to the back post that was met by Hunt and went in off the upright.

Walcott dinked a goal just before the break to give the Gunners a glimpse of hope going into the second half.

Reading came close to regaining a four-goal advantage just after the interval when first Robson-Kanu headed just wide before Ignasi Miguel almost skewed into his own net.

Mikele Leigertwood also went close before Walcott poked a left-footed effort against the post down the other end.

Arsenal were then denied a clear penalty when Chris Gunter knocked the ball away with his hand before substitute Olivier Giroud headed in a corner to pull another back.

The French forward was causing problems and he forced Federici into a acrobatic low save with a flicked header.

The game finished in a frantic fashion with chances at both ends and it was Arsenal who somehow managed to claw back to 4-4.

Koscielny headed home at the right end from a Walcott corner in the 89th minute before Walcott himself netted his second of the night by prodding just over the line deep into stoppage time.

The Gunners players celebrated their comeback wildly and Giroud and Francois Coquelin even threw their shirts into the crowd in celebration, not realising they had to play 30 minutes of extra time.

The first few minutes of the extra period were played out in a more relaxed manner after the dramatic late scenes before the visitors completed the turnaround through Marouane Chamakh.

The Moroccan forward linked up with Giroud and Andrey Arshavin down the left before firing through Kaspars Gorkss's legs and into the bottom corner.

Reading got back on level terms again in the second half of extra time when substitute Pavel Pogrebnyak headed home Hunt's deflected volley.

Arsenal had more gas left in the tank, however, and retook the lead as Walcott grabbed his hat-trick by smashing home from close range before Chamakh scored the 12th by lobbing with virtually the last kick of the game.

The draw for the fifth round takes place tomorrow night.