Superior finishing by Motherwell lifted them into third place in the Scottish Premiership as Kilmarnock continued their league struggle.
Home striker Kris Boyd spurned a decent chance in either half as he waited too long to shoot then headed over from close range.
His team-mate in goal, Craig Samson, tipped over a header by John Sutton.
But he was powerless to stop Sutton's diving header in 55 minutes or Henri Anier's composed finish late on.
Seven places and 13 points separated the lowly hosts and Motherwell, but Killie knew if they could better Ross County's result at Hearts, they would at least move up a place.
That would surely have gone down as progress for manager Allan Johnston, who is searching for a consistent, pleasing level of performance.
In Manuel Pascali and Stephen McManus both teams had straight-backed, resolute central defenders but it was the former who threatened in the opposition half early on.
The popular Italian aimed a firm header from 14 yards that Gunnar Nielsen in the 'Well goal had to be lively to catch.
Striker Sutton broke the deadlock with a header 10 minutes in the second half
But the visitors were gifted a chance when Northern Irish midfielder Sammy Clingan dithered on the ball and allowed Craig Moore to nip in on the edge of the box only to fire wide.
And Moore wasted two further chances as Kilmarnock struggled to clear their lines.
Clingan was involved in the play far more than his fellow midfielder Barry Nicholson and had the home fans applauding his effort from a free-kick that floated a fraction over.
Killie's attacking midfielder Chris Johnston set up the best chance of the first half for Boyd with an incisive pass down the inside-left channel. The striker shrugged off one challenge but tried to set himself too perfectly instead of shooting and the opportunity was gone.
That preceded a superb save by Samson. Fraser Kerr swung a perfect cross into the box and Sutton powered a goalbound header from 10 yards, which the Killie number one managed to tip over.
But parity lasted only 10 minutes after the restart. Iain Vigurs crossed low and Sutton seemed the only player with the desire to go for it as he dived headlong to nod home.
Kilmarnock come close to levelling immediately as Johnston snaked through the Motherwell defence and passed to Boyd, who set up Michael Gardyne.
His firm shot was parried by Gunnar Nielsen and there were no takers as Jeroen Tesselaar blasted a low ball across the face of goal on the rebound.
Clingan twice tried his luck from range with either foot before Gardyne lofted a beautiful cross for Boyd who, to Gardyne's disbelief, headed over from six yards.
Pascali's close-range header was gratefully grasped by the well-positioned Nielsen and it was clear by that stage that the next goal would be decisive.
That it should come for Motherwell upset the home fans who booed their team at the final whistle.
Anier, a replacement for Moore, took possession of the ball on the edge of the box, surged forward and made sure of the points with a cool, left-foot finish.
Consistency remains elusive for an increasingly embattled Johnston in the Killie dugout.
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