Theo Walcott's hat-trick helped Arsenal complete a remarkable comeback to stun Reading and book their place in the League Cup quarterfinal following an enthralling encounter at the Madejski Stadium.
Jason Roberts, Laurent Koscielny's own goal, Mikele Leigertwood and Noel Hunt had given Reading a four-goal first half lead.
But Theo Walcott's goal on the stroke of half time gave Arsene Wenger's side hope, before headers from substitute Oliver Giroud and Koscielny set up a grand stand finale
And after Walcott's shot, which replay showed had crossed the line, was followed up by Carl Jenkinson in stoppage time, the game was sent into extra time.
Marouane Chamakh's strike was cancelled out by Pavel Pogrebnyak's header, but with the game heading for penalties Walcott tapped in and Chamakh lobbed Adam Federeci to send Arsenal through and leave Reading dazed.
Having failed to win any of their eight games on their return to the Premier League, Reading were seeking some respite against an Arsenal side under pressure to add a first trophy since 2005.
The Gunners could have hit the front inside five minutes when Walcott miss-controlled a through ball, and he was made to pay as the hosts hit the front seven minutes later, as Roberts lashed home following Hal Robson-Kanu's cross.
The intensity which had accompanied Reading's Premier League displays was finally proving fruitful, and they doubled their lead when Garath McCleary's cross was turned into his own net by the returning Laurent Koscielny.
And Arsenal's fate was seemingly sealed before the break when Damian Martinez flapped at Leigertwood's stinging effort and Noel Hunt beat Jenkinson to McCleary's cross to send the home side into dream land.
Walcott cut the defect before the break, a mere consolation in the context of a first half which had seen the visitors dominated from start to finish.
However, Arsenal began the second half with added verve, and their halved the advantage with 26 minutes remaining as substitute Giroud headed home from Walcott's corner, with his first touch.
But The Royals stemmed the tide, as Federici saved twice from Giroud, but Koscielny's second of the night, at the right end, from another corner gave them hope going into four minutes of stoppage time.
Despite the time having elapsed, Walcott tricked his way through, with his shot seemingly having crossed the line prior to Nicky Shorey's hasty clearance, with Jenkinson netting from the rebound to cap a remarkable turnaround and set up extra time.
Come the additional 30 minutes, a shell-shocked Reading were helpless as Arsenal hit the front for the first time when Chamakh exchanged passes with Andrei Arshavin to fire home from 20 yards.
But Reading came again, and Pogrebnyak headed home with five minutes of extra time remaining, enough time for Walcott to thunder home to complete his hat-trick after Arshavin's mazy run, and Chamakh to lob Federici to send Arsenal through to the last eight.