Nine man Morton dug out a dramatic win on penalties as this Trust Trophy clash descended into chaos late on at Cappielow.
Ref Craig Napier flashed three reds as both sides were left infuriated at the whistler's performance.
But it was Ton who kept their cool to come through on penalties with only Ayr skipper Sean McGinty missing from the spot.
Lee Bullen had rung the changes with seven fresh faces into the starting line up, including a first start for David Bangala in a 4-3-3.
Josh Mullin and Brad Young also made their first starts since signing on loan earlier this month.
But United endured an uncertain start and were behind with the game just 12 minutes old.
The visitors couldn't clear their lines from a Morton free kick and when the ball fell to Lewis McGregor, his shot was deflected off Nick McAllister and past the helpless Aidan McAdams.
Ton came close to doubling their lead midway through the half but Alan Lithgow sent an overhead kick straight at McAdams from 12 yards.
At the other end, Sam Ashford had Ayr's first sight of goal with a driving run and shot which was straight at Brian Schwake.
But United were warming to their task and got the leveller just before the break when the impressive Young pulled back for Mullin to convert with a first time effort into the bottom corner.
Ton began the second half brightly and former United man Jack Baird forced a good save from McAdams with a header from a corner.
Jai Quitongo then fired inches past following another set piece, before Baird scooped over from underneath the bar as Morton pressed hard.
Then came the big flashpoints as both sides were reduced to ten men - decisions that sparked anger from all sides.
Paul Smith was first to walk for Ayr after a challenge on Lewis Strapp drew what looked to be a harsh second booking.
And just moments later, ref Craig Napier evened the odds with a straight red for Quitongo following a clash with Paddy Reading on the touchline.
Bullen turned to his bench, sending on Dipo Akinyemi, Mark McKenzie, Andy Murdoch and Mikey Hewitt as Ayr looked for fresh legs to win it.
And Akinyemi almost teed up McKenzie with a brilliant piece of play which saw the latter sting the palms of Schwake.
Then came more card drama as Baird was the next man to see red for Morton after hauling down Murdoch on the edge of the box with the Ayr man looking to home in on goal.
But Ton managed to negotiate the final moments with just nine men before coming through on penalties.
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