Kevin O'Brien scored a 50-ball century as Ireland chased down a target of 328 to upset England by three wickets at the World Cup.
O'Brien's effort was the fastest hundred in tournament history, all the more incredible given his side looked dead and buried at 111-5 shortly after his arrival at the crease.
He blasted 113 off 63 deliveries, including 13 fours and six sixes, and shared a 162-run stand in 17 overs with Alex Cusack (47) as England - for the third match in a row - lost the plot in the field.
O'Brien was run out with 11 still needed but John Mooney (33no) and Trent Johnston (7no) saw Ireland over the line from the first ball of the final over, Mooney finishing it in style with a boundary off James Anderson.
The result ranks as one of the great World Cup shocks - taking its place alongside Ireland's victory over Pakistan in 2007 and Kenya's wins against West Indies in 1996 and Sri Lanka in 2003.
It also blows Group B wide open and leaves England badly needing to bounce back straight away against South Africa on Sunday, while Ireland - who are also in action on Sunday against India - are firmly in control of their quarter-final destiny.
It had all been going so smoothly for England earlier in the day, Jonathan Trott becoming the equal fastest batsman to 1,000 ODI runs as they piled up their 10th highest total in the format.
Trott contributed a run-a-ball 92 to a score of 327-8 after England opted to bat first at Bangalore's M.Chinnaswamy Stadium, scene of their incredible tie against India last Sunday.
The Warwickshire batsman was playing just his 21st ODI innings, the same number required by team-mate Kevin Pietersen and West Indies legend Viv Richards to reach the landmark.
Pietersen also did his bit on the day, slamming 59 off 50 balls at the top of the order.
Ian Bell got in on the act, too, contributing 81 to a third-wicket stand of 167 with Trott before a late clatter of wickets saw medium pacer Mooney finish with 4-63.
Ireland's run chase got off to the worst possible start when skipper William Porterfield dragged the first delivery from Anderson (1-49) onto his stumps.
Porterfield's opening partner Paul Stirling dispatched five fours and a six in a cameo of 32 from 28 balls.
But his departure to a skier off Tim Bresnan (1-64) was followed by a triple strike from off-spinner Graeme Swann, who accounted for Ed Joyce (32), Niall O'Brien (29) and Gary Wilson (3) on the way to figures of 3-47 - the only English bowler to impress.
At the mid-point of the innings it seemed only a matter of time but Kevin O'Brien launched into a furious counter-attack, going to 50 off 30 balls with seven fours and three sixes.
And that was only the start as he required just another 20 deliveries to complete the sixth quickest hundred in ODIs - albeit helped by a life on 91 when Andrew Strauss, running back from extra cover, dropped a tough chance.
As had been the case against the Netherlands in their opeining match, England's fielding was well below-par - Cusack was also put down on 32, this time a difficult return catch for Michael Yardy (0-49), among five drops in all.
England finally made the breakthrough when Cusack failed to regain his ground after a mix-up over a single and, with 55 still needed from 51 balls, the match was still firmly in the balance.
But O'Brien knew he had done all the hard work and, in the company of Mooney, reined back the aggression and picked up easy ones and twos to reduce the equation to 12 required from the final two overs.
O'Brien was run out attempting to come back for two from the opening delivery of Stuart Broad's penultimate over, bringing Trent Johnston out to join Mooney.
Broad (0-73) promptly served up a full toss which Johnston drilled through the off side for four.
A scampered two and a pair of singles left three needed from the final over and Mooney completed the highest run chase in a World Cup with a boundary off Anderson's first ball.