Leicester came from two goals behind to secure a sensational 3-2 victory over Tottenham in the third round of the FA Cup.
Premiership Spurs had taken the lead through Jermaine Jenas before Paul Stalteri added a spectacular second.
But Elvis Hammond pulled one back for the Championship strugglers moments before half-time, Stephen Hughes hauled the Foxes level with an assured second-half strike and Mark de Vries bagged the stoppage-time winner.
It was the visitors who were on the offensive first as centre-half Michael Dawson released Aaron Lennon along the Spurs right.
His crossed from the byline but Rasiak was beaten to the ball at the back post by Leicester captain Paddy McCarthy.
The home side's response came in the seventh minute when De Vries saw his glancing header fly wide of target after Richard Stearman centred from the right wing.
• Match-winner feared the flag
Leicester threatened again soon after when a venomous De Vries shot was deflected wide off Michael Carrick's boot for an ultimately fruitless corner.
And the Dutchman should then have done better than miscue his shot into the stands after after rounding goalkeeper Paul Robinson.
Spurs opened the scoring in the 20th minute when a Carrick free-kick from the right drifted into the City box.
Keane headed to the far post and Jermaine Jenas prodded the ball home from six yards out.
De Vries muscled his way past Anthony Gardner but was denied by emergency defending from Michael Dawson.
And the former Hearts frontman was wide with a header from the resultant corner, taken by Ryan Smith.
Then, with a little less than 10 minutes until the break, Keane burst clear of the Leicester defence once more only to be denied by Douglas's save with the Republic of Ireland international then shooting wide after a ricochet from the goalkeeper's body.
The Leicester goal was under siege now and, ahead of the break, Keane fired over the bar and Michael Brown's low drive also went close.
Spurs' inevitable second goal came was blasted home by Stalteri who advanced along the right wing and powered a rising drive through the hands of Rab Douglas at his near post.
However, City pulled one back against the run of play when Hammond tapped home Stearman's supply with just two minutes remaining before the break.
Into the second half and both teams ran out unchanged with Spurs forced into some kitchen-sink defending within moments of kick-off as De Vries fed Stephen Hughes, whose low drive was blocked.
The Scotsman was quickly after the rebound and his persistence paid off when he hooked back into the danger area a ball which was apparently destined to bounce out of play with De Vries and then Smith also having efforts blocked.
With De Vries out to prove a point to his manager - who has made no secret of his dissatisfaction at the lack of goals at Leicester this season - the frontman brushed aside a challenge from Gardner but could only blaze high over Robinson's crossbar.
And, after all their pressure, Leicester had poor finishing from Stephen Kelly to thank after Spurs hit back on the break with Keane spraying a pitch-wide pass from left to right only for his team-mate to fluff his chance when faced with only Douglas to beat.
The Londoners were made to rue the miss as the home side drew level in the 57th minute with Spurs having failed to clear their lines following a Smith corner taken from the left.
And, after De Vries had flicked the ball on, Hughes, lurking on the edge of the penalty area, fired a sweet half-volley effort through a crowded penalty area and past unsighted England keeper Robinson.
The end-to-end pattern of this third-round encounter remained unchanged though as Spurs bounced back with Rasiak sending Keane clear only for Douglas to lash the ball into the stand.
And then Rasiak, a #2million signing from Derby during August, headed over after central defender Gardner had cut back from the Leicester byline.
England striker Jermain Defoe, on as a 70th-minute replacement for Brown, went close to scoring within just two minutes of his introduction as his quick feet created space in the Foxes' penalty area, only for his chipped effort to waft inches over the crossbar.
But then, in the first of three minutes' stoppage time, De Vries latched on to Joey Gudjonsson's pass and slotted a sensational winner from close range.
• 'We deserved it'
Leicester match-winner Mark de Vries admitted he was fearing an offside flag would rule out the late goal which dumped Tottenham out of the FA Cup.
TV replays showed De Vries was onside, and the assistant referee was also in no doubt.
'I thought he was going to say I was offside but obviously not,' De Vries told BBC1.
'I think if you work hard then you get your rewards. I think we deserved to win this one.'
Stephen Hughes, whose deflected strike dragged Leicester back to 2-2 in a game which Tottenham led 2-0, was delighted to claim the scalp of a team who stand fourth in the Barclays Premiership.
'Obviously everybody's loving it because in the league we've been threatening to score goals,' said Hughes.
Leicester are fourth-bottom in the Coca-Cola Championship, with relegation to League One a real threat, making the standard of performance they reached tonight all the more remarkable.
'Against Spurs, a top-class side, we knew it was going to be difficult,' said Hughes.
'I popped up with a goal which was brilliant and I think we deserved it.
'Credit to the boys and the manager and let's hope we can carry on into the league.'
Hughes recognised Leicester should be hitting such heights regularly.
'That's why the fans and everyone frustrated we know we can play like that. Let's hope that can kick-start our season.'
Substitute Elvis Hammond had started the comeback, replying to goals from Jermaine Jenas and Paul Stalteri.
'The manager made a change and I came on, got the goal, and it was the base for us to go on and win the game, which we did thanks to the winner from Mark,' said Hammond.
'Obviously it's nice for us to get a win over the Premiership boys. It's a good win for us.'