Theo Walcott completed a stunning comeback by Arsenal to dump Reading out of the Capital One Cup in the dying seconds of a night of high drama at Madejski Stadium.
Gunners outcast Marouane Chamakh, making his first start since January, appeared have secured victory with a fine strike in the 13th minute of extra-time.
With three minutes remaining Reading substitute Pavel Pogrebnyak equalised and it took Walcott's late goal and a second from Chamakh to end a thrilling tie.
Arsenal had fought back after going 4-0 down during a nine-minute first-half spell that left them shellshocked.
Jason Roberts, a Laurent Koscielny own goal and Mikele Leigertwood left home fans rubbing their eyes in amazement as Reading surged 3-0 ahead.
When Noel Hunt capitalised on yet more abysmal defending to stretch the lead to four, Arsenal were in danger of being overwhelmed by the inspired Royals.
But strikes from Walcott, the energetic Olivier Giroud, whose arrival from the bench brought urgency to the Gunners' play, and Koscielny offered hope.
Walcott was denied by a last-gasp save from Adam Federici in injury time.
The England winger appeared to stab home in the 96th minute but his effort was blocked.
Carl Jenkinson followed up to to guarantee extra-time by ramming home the loose ball.
With Arsenal now dominating the game - brilliant Reading were spent - there seemed to be only one winner until Pogrebnyak had his say.
The many visiting fans who left after Hunt had scored Reading's fourth will have missed one of their club's finest comebacks after a dire first half.
Reading made a bright start, but they could not have dreamed of the impending nine-minute spell that delivered three goals.
The first was beautifully worked with Hunt spreading the ball wide to Hal Robson-Kanu who picked out Roberts with a perfect low cross that the veteran striker smashed home.
There was more than a hint of luck over the second with Koscielny deflecting an attempt by Chris Gunter past Damian Martinez at the near post.
Barely had the Reading fans' celebrations ended before they were brought to their feet once more when Leigertwood powered the ball home in the 21st minute.
While Martinez should have saved the 20 yard effort - he got one glove to the ball - Arsenal were made to pay for the pedestrian defending in clearing a corner during the build-up.
Martinez continued to look uncertain as he gathered a long range shot by Hunt, who then delivered a fourth blow to the shellshocked Gunners.
Garath McCleary struck a hanging cross that fell to Hunt close to the far post and he outjumped Jenkinson before directing his header off the right post and into the net.
Chamakh and Emmanuel Frimpong were foiled as they sought to rescue a lost cause, but Arsenal seemed determined to assist Reading where possible with Jenkinson's back pass causing panic.
Respite finally arrived for the Gunners in first half injury-time when Walcott gathered Andrei Arshavin's pass and chipped keeper Federici.
The goal was nearly cancelled out shortly after the interval when Miquel Ignasi almost found his own net and then Leigertwood was guilty of wasting a reasonable chance.
Arsenal enjoyed a flurry of chances with Walcott and Serge Gnabry going close, before Chamakh had a penalty turned down and was subsequently booked for demonstrating to the linesman.
The visitors were spending more time on the ball and were rewarded when substitute Giroud nodded home in the 65th minute.
Giroud almost grabbed a second but was denied by a super save from the diving Federici.
Reading's defence was under enormous pressure as they dealt with waves of Arsenal attacks and they cracked with two minutes remaining when Koscielny headed in a corner.
The fingertips of Federici appeared to have prevented Walcott from taking the match into extra-time, but the Arsenal were level in the 96th minute.
Defender Nicky Shorey was on hand to stop the ball crossing the line but Jenkinson smashed it home.
Giroud and Arshavin combined to send Chamakh racing in on goal and he showed his gratitude by steering the ball beyond Federici.
But neither a roller-coaster match nor Reading were finished as Pogrebnyak nodded in a cross by Chris Hunt with three minutes remaining.
Walcott and Chamakh then struck in the dying moments of the match, concluding a heart-stopping night.