Jon Daly suffered a blow in his attempts to secure the Hearts head coach's job permanently as Motherwell earned a 2-1 win over the Tynecastle side.
Ryan Bowman and Louis Moult scored to overhaul Kyle Lafferty's opener for Hearts, leaving owner Ann Budge with a decision to make next week.
Budge plans to appoint a new manager in the next few days and Under-20 coach Daly is competing with Steven Pressley and Paul Hartley for the position. After a win over Kilmarnock and a goalless draw against Rangers, defeat at Fir Park was a disappointment for the Irishman in interim charge.
Lafferty scored an impressive opener before Bowman's header and Moult's stunning effort into the top corner gave Motherwell the advantage at half-time. They were the stronger team in the second half, with one effort cleared off the Hearts goal line and another disallowed for offside.
Hearts arrived in Lanarkshire with four points from their last two games and not a goal conceded. They brought 2,419 fans from Edinburgh in a crowd of 6,568. Cole Stockton was given his first start since joining the club against a Motherwell team which had won six of their eight competitive fixtures since the season began.
Motherwell appealed strongly for a penalty in the opening minutes when Elliot Frear's shot struck the visiting full-back Michael Smith. Hearts then made their own claim at the opposite end when Rafal Grzelak was pushed in the back by Ryan Bowman. Referee John Beaton was unmoved on both occasions and the frenetic start to the match continued apace.
The tempo began to settle somewhat as the half-hour mark approached. Jamie Walker forced a save from the Motherwell goalkeeper Trevor Carson before the visitors took the lead. Lafferty, as he had done several times already in this match, picked up possession and drove deep into opposition territory. From 25 yards out, he drove an accurate low shot away from Carson and into the corner of the net.
Hearts' advantage lasted only seven minutes. Richard Tait's right-wing cross found Louis Moult at the back post for a headed cutback and, with defenders static, Bowman calmly nodded the ball into the net for his first goal at Fir Park.
Motherwell had only just finished celebrating their leveller when they moved ahead. Walker was dispossessed near the edge of his own penalty box and the ball broke to Moult. He produced an exquisite first-time finish to angle the ball over Hamilton and into the top corner.
Both No 9s, Lafferty and Moult, were the outstanding players afield but there was no question Daly needed more from others to claw back the 2-1 interval deficit. Walker responded on 58 minutes. He picked up the ball and ghosted past three opponents before his final 22-yard shot was deflected for a corner.
However, Motherwell could easily have gone 3-1 up moments later. Moult's header at the back post was cleared by Christophe Berra on his own goal line as the home players and fans appealed that the ball had crossed the line. Beaton and his assistants allowed play to continue, much to the hosts' frustration.
Another Bowman header from close range landed in the Hearts net but the offside flag ruled the effort out. Steve Robinson's side were in command at that stage but found themselves under pressure as the final whistle neared. Hearts put a series of cross balls into their opponents' box, but they stood firm to see out the game.
Motherwell (3-5-2): Carson; Kipre, Heneghan, Dunne; Tait, Cadden, McHugh, Rose, Frear; Moult, Bowman.
68: Campbell for Frear
79: Fisher for Moult
Unused subs: Griffiths, Bigirimana, Plummer, MacLean, Tanner.
Hearts (4-4-2): Hamilton; M Smith, Souttar, Berra, Grzelak; Cowie, Randall, Djoum, Walker; Stockton, Lafferty.
60: Goncalves for Stockton
79: Buaben for Randall
79: Moore for Walker
Unused subs: McLaughlin, Hughes, Currie, Brandon.
Referee: John Beaton.