Captain Brad Lyons marked his return with the decisive goal as Kilmarnock overcame Dundee United to book a Premier Sports Cup quarter-final clash at home to St Mirren.
In sweltering conditions at Rugby Park, Marcus Dackers put Killie ahead early on, racing onto Ben Brannan’s precise long pass before drilling past Yevhen Kucherenko.
United’s problems deepened when striker Max Watters was forced off through injury after just 17 minutes.
Yet his replacement, 18-year-old Owen Stirton, made an instant impact.
The youngster collected a pass from Amar Fatah, twisted away from his marker, and coolly finished into the far corner to level the match eight minutes later.
Fresh from a gruelling midweek penalty-shootout defeat to Rapid Vienna in Conference League qualifying, fatigue soon crept into United’s play.
Fatah, symbolic of their tiredness, squandered a good opening by dragging a shot wide from inside the box.
Brannan came close to restoring Kilmarnock’s advantage with a curling effort that flashed narrowly over, but it was Lyons who ultimately settled the contest.
The skipper reacted smartly to Lewis Mayo’s knockdown, volleying through Kucherenko’s legs to seal Killie’s progression.
Kilmarnock manager Stuart Kettlewell: "When I came in on day one, if you'd offered us this start [to the season], we would have bitten your hand off.
"We had a bit of control in the game, created one or two chances but then I felt we sank. We gave them some sort of incentive and were disappointed to be pegged back. The players responded well and overall I felt we deserved to win."
Dundee United manager Jim Goodwin: "We always had a concern about this afternoon's fixture given the exploits on Thursday night.
"The boys have played 120 minutes of football on Thursday, very little time to recover for the game, Kilmarnock were the fresher team and I think that showed. But that's no excuse for some of the goals we conceded.
"The first goal was shocking, the second goal is embarrassing. We've had numerous warnings in the last couple of games, we've not dealt with a wide free-kick."
