Goals in each half from Andy Halliday and Liam Boyce brought the Edinburgh club a second successive league win following last week’s opening victory over Celtic.
Joe Shaughnessy headed St Mirren’s consolation before substitute Kristian Dennis was sent off for lashing out at Peter Haring in a dramatic ending.
For Hearts, this was a momentous victory after nine years without a win on St Mirren’s pitch. Their last victory here was a 2-0 Scottish Cup success back in 2012 but they left top of the league ahead of Sunday’s fixtures.
They arrived without Stephen Kingsley due to illness. Haring was the replacement, the Austrian deployed in midfield with Halliday shunted out to left wing-back and Alex Cochrane playing left of the three-man defence.
Saints drew 2-2 at Dens Park in their opening match and reinstated Greg Kiltie to support strikers Curtis Main and Eamonn Brophy.
Just over 1,000 home fans were present inside the SMISA Stadium to witness an early moment of controversy. Hearts winger Gary Mackay-Steven was floored by an apparent elbow which went unpunished.
The visitors exacted their own form of retribution by scoring first on 17 minutes. Beni Baningime fed Liam Boyce on the left of the St Mirren penalty box, and his low ball inside was superbly scooped into the far corner of the net by Halliday.
The locals grew increasingly frustrated with referee Gavin Duncan during the first half as he curtailed several home attacks by whistling for fouls against black-and-white shirts.
Jamie McGrath was the best player afield with a series of probing passes turning the Hearts defence. His corner was headed over the crossbar by Joe Shaughnessy ten minutes before half-time.
St Mirren finished the first half strongly and Main twice tested Craig Gordon early in the second as the hosts continued moving the ball well. Their opponents from Edinburgh were doing the chasing at that point.
Greg Kiltie zipped a ball across goal and Main sent an acrobatic attempt wide of target as the pressure increased. Robbie Neilson, the Hearts manager, received a caution midway through the second period for protesting about a late challenge by Charles Dunne on Mackay-Steven.
Hearts forced their way forward to settle this contest on 73 minutes. They moved the ball across the edge of St Mirren’s penalty area to Boyce, who switched it from left foot to right and dispatched a 20-yard drive home.
Goalkeeper Jak Alnwick seemed to react slowly but Boyce was instantly off celebrating his first league goal of the campaign.
Substitute Aaron McEneff unleashed a 30-yard shot which clipped the outside of Alnwick’s left post before Shaughnessy’s late header from McGrath’s cross halved the deficit.
At kick-off, Dennis senselessly ran past Haring and threw out an arm to prompt an instant red card from referee Duncan. Hearts saw the game out and would have scored a third but for Alnwick’s terrific late save from Michael Smith.
St Mirren (3-4-1-2): Alnwick; Fraser, Shaughnessy, Dunne; Tait (Henderson 77), McGrath, Power, Tanser; Kiltie (MacPherson 77); Main, Brophy (Dennis 77).
Hearts (3-4-3): Gordon; Souttar, Halkett, Cochrane; M Smith, Haring, Baningime, Halliday; Ginnelly (Gnanduillet 64), Boyce (Henderson 88), Mackay-Steven (McEneff 76).