Goals from Curtis Main and Alex Gogic were enough to secure victory for St Mirren at Tynecastle on Saturday as they closed the gap on Hearts to a single point.
The result also proved to be the final nail in the coffin for Robbie Neilson's latest stint as Jambos manager.
He came under heavy fire from furious supporters as his team crashed to a fifth defeat in a row, with his departure confirmed by the Edinburgh club on Sunday.
Buddies boss Stephen Robinson picked the same starting 11 that had lined up for the 3-0 home win over Livingston the previous weekend.
And it was the visitors who had the first sight of goal in the ninth minute at Tynecastle but Joe Shaughnessy headed wide from Thierry Small's corner.
After a slow start, Hearts started to crank things up and captain Lawrence Shankland saw a shot from just inside the box deflected behind.
At the other end, Gogic threatened when he connected with another Small corner and saw his downward header hit the turf and bounce up over the bar.
Hearts struggled to create clear chances but they finished the half strongly and almost conjured an opener in the 42nd minute when Andy Halliday headed Stephen Kingsley's cross against the bar.
Halliday and Jorge Grant then both threatened with headers in the closing moments of the half.
The Jambos had a great chance to take the lead in the first minute of the second period when Kingsley's pass across the St Mirren penalty area found Michael Smith in space but the right-back's shot from 15 yards out was well saved by keeper Trevor Carson.
Saints continued to be a threat, though, and Australian midfielder Keanu Baccus fizzed a shot over from just inside the box in the 49th minute.
Two minutes later, Gogic glanced a header wide from substitute Scott Tanser's cross.
The visitors took the lead in the 52nd minute when Kye Rowles failed to deal with a ball over the top, allowing Main the space he needed to rifle in a superb left-footed shot from 20 yards out.
St Mirren doubled their advantage five minutes later as a long throw from Shaughnessy caught out the Hearts defence.
Mark O'Hara pounced on the ball from eight yards out and his strike deflected off Gogic and into the net.
The exasperated home support responded by chanting for Neilson to go.
Things got worse for the Jambos in the 62nd minute when Robert Snodgrass, who had been booked for a bad tackle in the first half, was shown a second yellow for a challenge on Main as the St Mirren forward tried to burst clear down the left.
Television replays suggested the former Scotland midfielder had actually won the ball but, as he disappeared down the tunnel, so did any chance of Hearts fighting their way back into the game.
The full-time whistle was greeted by loud jeers from the Gorgie fans and Neilson was heckled by a large section of supporters as he walked on to the pitch to shake hands with the officials.
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