A 90th minute header from Stephen Pearson gave Motherwell their first win of the season and proved that they can survive without their talisman and star performer James McFadden.
The Scotland forward had earlier fired them ahead from the penalty spot, but such is his influence that ten-man Kilmarnock drew level through defender Frederic Dindeleux within two minutes of McFadden being substituted.
But instead of feeling sorry for themselves, Motherwell kept scrapping right to the final whistle and were rewarded in the dying seconds when slack marking at a corner kick allowed Pearson to pick his spot with a powerful looping header.
Motherwell began the afternoon both pointless and goalless after their opening two SPL fixtures although the return from injury and suspension of McFadden and Derek Adams clearly gave them an instant lift.
They quickly put a weakened Kilmarnock side minus five first-team regulars under pressure with Alex Burns and Pearson continually posing problems and Keith Lasley seeing a stinging drive blocked.
It remained one-way traffic for most of the first half as Burns, Lasley and McFadden all tested goalkeeper Colin Meldrum from the edge of the box. In reply Killie could manage a long-range free-kick which flashed wide and a team header from Barry McLaughlin.
Motherwell kicked off the second period by launching a dazzling counter-attack and it required an excellent save from Meldrum to deny Adams. Meldrum did it again in the 63rd minute, saving at the second attempt from Pearson as Adams moved in for the rebound.
The pressure eventually told just three minutes later when defender James Fowler was forced to handle on the line after McFadden finally squeezed the ball past Meldrum.
McFadden's successful penalty and a red card for Fowler appeared to kill off Kilmarnock's chances but a snapshot into the side netting from substitute Colin Nish proved they were still a threat.
Dindeleux's headed equaliser looked to have secured them an unlikely point until that last gasp winner from Pearson.