Kilmarnock won the Scottish Communities League Cup for the first time in their history and ended Celtic's hopes of winning the domestic treble.
Celtic's Gary Hooper, Anthony Stokes and Scott Brown and Killie's Dean Shiels and Paul Heffernan all had efforts saved in a frenetic first half.
Killie keeper Cammy Bell denied Stokes and Victor Wanyama after the break.
Dieter van Tornhout headed Kilmarnock ahead six minutes from the end and Celtic could not find a leveller.
Having lost in the final of this competition on five previous occasions, Killie were also trying to win their first trophy since 1997's Scottish Cup triumph.
Scottish Premier League leaders Celtic were looking for a 15th tournament win, with Neil Lennon's side also still in the Scottish Cup.
Mahamadou Sissoko presented Hooper with an early chance on the edge of the penalty area but Bell made an excellent save to spare his team-mate's blushes.
The Ayrshire side weathered the early storm and offered a threat when they moved forward, Shiels sweeping a low drive round the post after getting the break of the ball on the 18-yard line.
Bell made another impressive save to deny Stokes after the striker met Brown's cross with a powerful downward header.
At the other end, Shiels cut in from the left and drew a save from Fraser Forster before Sissoko's header from the resulting corner was cleared near the line by Stokes.
A rasping 20-yard drive by Brown was tipped over by Bell before Forster was called upon to keep his side level.
Paul Heffernan was played in on the right-hand side of the box and the striker set himself before unleashing a shot but the keeper spread himself well to block.
Shiels missed an excellent chance right at the start of the second after bustling his way through a ruck of players into the area, the forward mis-hitting his shot wildly across the box as Forster closed him down.
Minutes later, a Killie corner was cleared and then returned into the box and Sissoko headed wide from a good position.
Celtic regained the ascendancy and Joe Ledley dragged a shot wide before Stokes fired into the hands of Bell after working space inside the area.
Bell made another important save when Wanyama rose to meet James Forrest's corner and Kilmarnock's Gary Harkins soon made way for van Tornhout.
With the match entering its final 15 minutes of regulation time, James Fowler flashed a shot over the Celtic goal and Heffernan had another effort blocked by Forster.
Bell came off his line to smother the ball after Charlie Mulgrew had dribbled his way into the penalty area.
And the goalkeeper's heroics were rewarded as Killie soon moved into the lead with a determined counter-attack.
Ben Gordon released substitute Lee Johnson on the left and his whipped cross was headed into the net by van Tornhout at the back post, the Belgian's first goal for Kilmarnock.
Celtic chased a leveller and Bell made a double save to deny Georgios Samaras and fellow replacement Kris Commons.
As the match entered injury time, Stokes burst through on goal and went to ground as Michael Nelson challenged but referee Willie Collum waved away penalty claims and booked the Celtic striker.
And Kenny Shiels' side held on in injury time to claim the Cup.