Kilmarnock had been by far the better side for 75 minutes, building a comfortable two goal lead and threatening to run riot. Only a series of brilliant saves from Ludovic Roy kept Ayr in the game, and they fully capitalised with two goals in quick succession in the final fifteen minutes.
Alan Combe made his debut and performed creditably in difficult goalkeeping conditions, while Gary Wales and Peter Leven were both introduced from the bench.
The match began quietly before David Lilley nodded Stevie Murray's corner home from close range in the 25th minute. This gave Killie confidence and their SPL quality began to show, and for long spells it was simply too much for the Second Division side.
Kris Boyd twice beat the offside trap, first dragging his shot wide before rounding Roy but the angle closed on him before he could get his shot on target.
Killie should have had a penalty in the 36th minute after Murray jinked into the box and stood a cross up at the far post. Boyd acrobatically kept the ball in play as he bicycle kicked the ball into the six yard box, but as Gary MacDonald went in to bundle the ball home, defender David Craig clearly punched the ball away from goal, but referee Jamie Downie, who had a clear view of the incident, kept his whistle silent.
Rhian Dodds and Gary Locke snuffed out the Ayr midfield allowing their full backs to power forward, with Garry Hay in particular enjoying himself on the left hand side. In a typical run ten minutes into the second half, Hay reached the six yard line and shot for the top corner only for Roy to block superbly.
The second goal was only delayed six munites however. United's Marc Smyth misjudged a high ball as it got caught in the stiff breeze and Craig Dargo stole possession on the half way line. He laid the ball off to Murray and sped forward and received the perfect return ball into his path for the lively striker to coolly slide the ball home.
It was almost three two minutes later when Boyd and Dargo combined to tee Murray up, but the winger's flick cleared the crossbar.
Killie gave Gary Wales his first outing when he replaced Dodds in midfield, but the match turned around in the 78th minute.
Stewart Kean got the better of Lilley inside the box and drilled a low shot past Combe and Ayr drew level three minutes later when ex-Killie man Darren Henderson's drive was parried by Combe and Graeme Brown snapped up the rebound.
The match went straight to a penalty shoot-out and only Wales failed to convert his spot-kick, Roy diving smartly to his left to save. It was no surprise that Barry McLaughlin signed from Killie in the summer stepped forward to score the winning goal.
Kilmarnock: Combe; Fowler, Lilley, Dindeleux, Hay; MacDonald, Dodds (Wales), Locke, Murray (Leven), Boyd, Invincibile (Dargo). Unused subs, Canning, Naismith, Smith
Killie retained the Old Crocks trophy as Willie Watters eased down the waistband and rolled back the years with a delicious winner, adding to Mark skilling's opener in a 2-1 success.