Motherwell defender Stephen Craigan's joy at signing a new contract quickly turned to despair as his own goal handed Hearts victory at Fir Park.
Hearts dealt better with a strong wind as Motherwell suffered a blow to their hopes of Uefa Cup qualification.
But Well were enraged that Eggert Jonsson's 11th-minute drive, deflected in by Craigan, took place as David Clarkson was down with a head knock.
Craigan was denied an equaliser by a fine save from goalkeeper Steve Banks.
Motherwell had gone into the game four points clear of fourth-top Dundee United.
Stephen Hughes returned to the midfield - replacing Darren Smith - after being ruled out of the midweek victory over Inverness with a knee injury.
Hearts were missing top scorer Andrius Velicka, who is expected to sign for Norwegian side Viking FK next week, with a pelvic injury.
MY SPORT: DEBATE
Andrew Driver failed to recover from a groin injury, while fellow midfielder Audrius Ksanavicius dropped to the bench.
And Christian Nade, Calum Elliot and Lee Wallace came into a starting line-up that immediately threatened the home goal.
But goalkeeper Graeme Smith beat away Nade's shot from 12 yards after Deividas Cesnauskis' driven corner was missed by Motherwell midfielder Marc Fitzpatrick.
Wallace flashed an effort wildly over the crossbar from the edge of the box after being set up by Cesnauskis.
However, the visitors soon took the lead in controversial circumstances.
Motherwell striker David Clarkson lay in the Hearts penalty area with a head knock following a clash with Tynecastle defender Jose Goncalves.
But referee Craig Thomson refused to stop play as Hearts sprung a counter-attack.
The move finished with midfielder Jonsson's wayward drive from 25 yards being deflected past Smith by Fir Park skipper Craigan.
A groggy Clarkson had to be replaced with Simon Lappin on the half-hour mark.
And Hearts looked the more steady side despite playing against the breeze.
The Motherwell fans showed their frustration by chastising referee Thomson over every decision as their side failed to threaten Hearts' goal.
And home manager Mark McGhee directed his own strong words at the official during the half-time break.
Hearts continued to threaten and Craigan was fortunate that another deflection did not lead to a second own goal.
Craigan's nightmare continued as he was shown a yellow card for a foul on Wallace.
Motherwell threatened from their first corner of the match, but Marc Fitzpatrick headed wide from Ross McCormack's dangerous cross.
And Craigan was denied by Banks after meeting a McCormack free-kick with a flashing header.
The goalkeeper parried the resulting corner straight at the feet of two Motherwell players but recovered to save and win a free-kick in the resulting goalmouth melee.
Craigan was replaced with Danny Murphy with six minutes remaining as the home side pressed for an equaliser, but Banks was on hand again to deny Lappin.
Motherwell: Graeme Smith, Quinn, Craigan (Jamie Murphy 84), Reynolds, Hammell, Hughes (Darren Smith 55), Lasley, Fitzpatrick, Clarkson (Lappin 30), Porter, McCormack.
Subs Not Used: Daniels, Brian McLean, Danny Murphy, Archdeacon.
Booked: McCormack, Craigan.
Hearts: Banks, Neilson, Berra, Goncalves, Wallace, Cesnauskis (Mikoliunas 73), Jonsson, Palazuelos, Karipidis, Nade (Beniusis 83), Elliot (Zaliukas 89).
Subs Not Used: Basso, Thomson, Ivaskevicius, Ksanavicius.
Booked: Elliot, Jonsson, Mikoliunas.
Goal: Craigan 12 og.
Att: 5,925
Ref: C Thomson
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