Late goals from Paul McGowan and Conor Newton secured St Mirren just their third away win of the season as they rounded off their Clydesdale Bank Premier League campaign with three points at Rugby Park.
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In the Buddies' three previous attempts to overturn Kilmarnock this term, the best they had managed was two draws, but they finally overcame Kenny Shiels' side with McGowan's spot-kick success 15 minutes from time ahead of a late Newton effort.
John McGinn, had put Danny Lennon's side ahead with his first senior goal after 20 minutes but Kris Boyd levelled soon after for the hosts.
Killie's unbeaten record against the men from Paisley was ruined, however, with McGowan and Newton's late intervention.
The line-ups of both sides were more notable for the players who would be moving on than staying put, with Killie starting Rangers-bound goalkeeper Cammy Bell and former Scotland striker Boyd, who is also expected to exit this summer.
St Mirren boss Lennon, meanwhile, allowed contract rebel Craig Samson and released striker Sam Parkin to join the on-loan trio of Paul Dummett and Newton, both borrowed from Newcastle, and Rio Ave forward Esmael Goncalves for one final outing before they all say their goodbyes.
It was another possible Saints player who could be making his departure, Kenny McLean - tipped for a close-season move to the npower Championship - who came up with the first effort on goal but his scissors kick from McGinn's corner was well off target on 16 minutes.
The supplier of that first chance made no mistake four minutes later, however, when presented with a more straight-forward attempt.
Newton drove to the by-line on the right before crossing to McGinn at the back post and it was a perfect assist as the young midfielder did not even have to break stride to volley home with power from five yards out.
The visitors' lead last just five minutes as Perez found a chink in the Buddies defence to play through Boyd.
St Mirren centre-halves Jim Goodwin and Marc McAusland had stepped up but full-back colleagues David van Zanten and Dummett failed to read the signal, playing the Killie attacker on as he raced through on goal.
Keeper Samson didn't help matters by darting from his goal before hesitating allowing Boyd to poke the ball home.
Chances were more limited in the second half although Newton did see a deflected strike fly just over Bell's frame early on, while Boyd nodded wide from teenage winger Chris Johnston's corner after 73 minutes.
Within two minutes of that miss though, Killie shot themselves in the foot.
It was 19-year-old defender Lee Ashcroft's youthful exuberance which got the better of him as he slid in on another youngster, the Buddies' substitute Anton Brady - also 19 - in the box when there was no immediate danger to concede a needless penalty, which was ruthlessly dispatched by McGowan.
With two minutes left, Newton signed off after a successful six-month spell in Scotland with just his second goal for the club following his strike against Hearts in the team's 3-2 Scottish Communities League Cup win in March.
With Killie tiring, he was allowed to dance past three half-hearted tackles before poking the ball past Bell to wrap up the victory.