Scott Rendell's late strike stunned Premier League Norwich City as Luton Town became the first non-league team to knock a top-flight side out of the FA Cup since 1989.
The substitute's near-post effort with 10 minutes remaining capped off a monumental display from the Hatters.
Norwich missed decent chances through Grant Holt and Leon Barnett.
But Blue Square Bet Premier side Luton held firm after Rendell's goal to dramatically reach the fifth round.
Non-league minnows beating a top-tier side is a feat unheard of since 1989, when Sutton United of the Conference toppled Coventry City 2-1 in the third round.
Luton, unlike Sutton, are steeped in Football League history, but this result will be considered one of the great upsets purely for the fact that it was played out on the Premier League club's own turf.
These two sides were in the same division just six years ago, facing each other in the Championship, but three successive relegations and a raft of financial problems led to the Hatters' dramatic and swift decline, to the point that they are now in their fourth season in the Blue Square Bet Premier.
But Paul Buckle's side, slayers of Championship Wolves in the third round, belied the 85 places between themselves and their hosts.
This was no smash and grab win - it was fully deserved.
Luton started strongly, pushing high up the pitch and pinning the Canaries back, but had few chances to show for their dominance.
Norwich, lacklustre in the opening 30 minutes, improved and had opportunities through Simeon Jackson and Harry Kane before Leon Barnett struck a post and saw his rebounded effort cleared off the line.
The Hatters, beaten FA Cup finalists in 1959, were resolute though and coped with the powerful presence of striker Grant Holt, who was brought off the bench at half-time by a desperate Norwich boss Chris Hughton.
Holt did come close, heading at keeper Mark Tyler at the back post and teeing up Simeon Jackson but his effort went straight at the keeper.
However, Luton not only soaked up Canaries pressure, they showed intent of their own, and as the game drew on, and Norwich poured further forward in an attempt to avoid a replay, the visitors were finding space to break into.
Alex Lawless, the goalscoring hero against Wolves, came close, but, with 10 minutes remaining, the Hatters were in dreamland.
JJ O'Donnell steamed into the left channel and fizzed a ball into the near post; substitute Rendell, a journeyman of lower-league sides including Cambridge United and Torquay, applied a deft touch and the ball nipped past Declan Rudd and into the net.
The Canaries, visibly rattled, lacked composure as they searched for the goal to spare their blushes.
But Luton, with Janos Kovacs reassuringly solid at the centre of defence, held strong against a series of balls into the box.
They got the luck they deserved when referee Andre Mariner missed Lathaniel Rowe-Turner's handball in his own penalty area.
And after four minutes of injury time, the side who have spent four seasons trying to regain Football League status, were on their way into the fifth round.
Norwich, whose only win in their last seven games came in the last round of this competition at Peterborough, have worrying problems to address as they look to avoid Premier League relegation.
But the scenes of jubilation from Luton's fans, players and staff, showed that this was truly their moment.