Jim Goodwin fired a superb 35-yard strike beyond Jamie McDonald seven minutes before half-time to give the hosts the lead.
And Lewis Guy doubled their advantage three minutes after the interval after a lightening fast counter-attack ended with Steven Thompson cutting the ball back for the striker to blast into the net.
The visitors pushed men forward in an effort to find a way back into the game, however they struggled to test Craig Samson in the St Mirren goal.
Buddies manager Danny Lennon handed a first start to on-loan defender Paul Dummett, while Ryan Stevenson made his first start for the visitors since making his return to Tynecastle.
Goodwin was booked inside the opening minute when referee Calum Murray adjudged him to have lunged in studs-up on Darren Barr.
The visitors created the first real chance of the match after eight minutes when Callum Paterson headed Arvydas Novikovas' assist across goal.
The 17-year-old came even closer a minute later when he raced through on goal before firing a low effort on goal which Samson did well to turn away for a corner.
St Mirren responded in a positive fashion and Paul McGowan passed up a glorious chance to open the scoring when he connected with David Van Zanten's pin-point cross, however the striker headed wide from just six yards.
Paterson passed up his third opportunity of the opening half hour when Novikovas took advantage of some hesitancy by Van Zanten and cut the ball back along the six-yard box.
It looked like a goal was sure to follow but he was denied by an excellent block by Dummett.
Dummett was enjoying an eventful first start for St Mirren and two minutes later he was involved at the other end when his low cross was met by Guy, forcing McDonald to make his first save of the match.
The deadlock was finally broken seven minutes before the interval and the home fans are unlikely to forget Goodwin's wonderful strike. He collected the ball 35 yards from goal and unleashed a low effort which beat McDonald and nestled in the bottom right-hand corner.
Hearts began the second half on the front foot but found themselves 2-0 behind after 48 minutes.
Marc McAusland orchestrated a quick breakaway and Thompson burst through the challenge of Barr before unselfishly rolling the ball to Guy, who blasted the ball into the empty net.
Lennon made his first change of the match when Gary Teale replaced Graham Carey after 55 minutes.
As the visitors threw men forward in search of a way back into the game, they left themselves vulnerable on the counter-attack and the Hearts defence breathed a sigh of relief when Guy strayed offside when attempting to connect with McGowan's dangerous cross.
Danny Grainger's corner almost caught out Samson on 63 minutes and the keeper was relieved to see the ball sneak past his right-hand post.
Hearts boss John McGlynn replaced a defender with a striker as Barr made way for John Sutton with 25 minutes remaining.
The attacking switch did little to change Hearts' attacking threat and McGlynn responded again by introducing Dale Carrick for Andy Driver.
St Mirren made a change of their own at the same time as the tiring Carey was removed for Dougie Imrie and with eight minutes remaining Sam Parkin replaced Thompson.
McGlynn continued to urge his men forward as the fourth official Iain Brines indicated three additional minutes, but his side were unable to create any chances of note and St Mirren held out for a comfortable win.
