Motherwell moved a point clear of Celtic at the top of the Scottish Premier League as Hearts' discipline problems continued under Paulo Sergio.
Hearts had Ian Black sent off after 50 minutes after a reckless tackle on Keith Lasley.
And they were made to pay 12 minutes later, when Jamie Murphy rounded goalkeeper Marian Kello to score.
Lasley was also sent off three minutes from time, but Sergio suffered defeat in his first domestic game in charge.
The new manager, who took over from Jim Jefferies last week, was unable to end a run without a league win that has now stretched to 11 games.
For Motherwell, it was a deserved second home win of the season for Stuart McCall's team, although they were given some assistance by a Hearts side who were handed a record £100,000 fine following last season's continued on-field indiscipline.
Michael Higdon had returned from a thigh injury to lead the line for Motherwell, while Steven Saunders was restored to the defence as Robert McHugh and Shaun Hutchinson dropped out.
Sergio, who led Hearts to Europa League victory on Thursday, handed Jamie Hamill his SPL debut following suspension and the wide man replaced the injured Stephen Elliott.
It was the visitors who were first to threaten when Andrew Driver robbed the careless Saunders and sent in a drive that Motherwell goalkeeper Darren Randolph did well to push behind for a corner.
It was Kello's turn to pull off a good save from Steve Jennings, who had picked up a Chris Humphrey cross at the far side of the box.
In-demand Motherwell striker Murphy squandered the best chance of the first half when he appeared to mis-time his jump and headed Humphrey's cross over the bar from six yards.
Randolph had to rush from his goal to deny Driver after a sliced clearance from Saunders put the home side in trouble.
The Motherwell keeper was forced into another save, this time from Hamill's long-range effort that threatened to sneak in at his left-hand post before the interval.
Hearts were reduced to 10 men when Black, once again showing a short fuse that has hampered his career, went through midfield rival Lasley.
Instead of shutting up shop, Sergio brought on former Motherwell striker John Sutton in place of winger Driver.
However, it was the home side who began to take control and Murphy and Stevie Hammell both squandered chances before the breakthrough finally came.
Eggert Jonsson's poor positioning played Motherwell onside as Nicky Law picked out Murphy and the Scotland Under-21 forward supplied the cool finish.
Tom Hateley sent a dangerous ball flashing across the face of the Hearts goal and Kello turned a Murphy header round the post as Motherwell came close to extending the lead.
Lasley was shown a second yellow card for a late, tired challenge on Arvydas Novikovas, but Well safely negotiated the closing minutes.