Gerald Taylor (82) headed into his own net for the opening goal
Head coach Steven Naismith is sure he can arrest Hearts' alarming slump after an eighth successive loss away to St Mirren kept the Edinburgh club at the foot of the Scottish Premiership.
Poor defending at set-pieces was the theme in Paisley. Both teams scored from their first corner kicks, with Gerald Taylor losing his bearings when trying to mark Richard Taylor and heading Mark O'Hara's delivery into his own net.
Hearts levelled soon after as Craig Halkett glanced home a flat cross from Blair Spittal.
The visitors were looking the more menacing side but more slack play at the back handed the initiative to St Mirren.
On 34 minutes, Killian Phillips nodded on a long free-kick and Toyosi Olusanya was quickest to the loose ball, lashing it high into the net.
Olusanya fired the wrong side of the post from close range early in the second half, Kevin van Veen whistled a couple of efforts wide, and Roland Idowu was denied by Craig Gordon as St Mirren registered their first Premiership victory since the opening weekend.
Hearts barely mustered a chance after the interval and remain rooted to the bottom of the table, without a win this season.
"I fully believe I can," Naismith told BBC Scotland when asked if he can rediscover the form that earned a third-place finish last term. "I wouldn't be here if I didn't.
"My relationship with the club and board is very good. I've said that if I feel I've lost the players or the players had lost what we are wanting, I'd walk away, but I don't think we are at that point.
"Small parts of the game are costing us but I'm definitely up for the fight. In these moments, you learn a lot. We can put a good run of form together.
"There's no better club for me to be at. But I understand fans' opinions are going to be strong, we heard that today.
"The club are understanding. They'll make the right decisions at the right time."
St Mirren make power pay
St Mirren fans may have been a bit nervous since they led 2-1 at the break in their last two matches only to draw them both.
However, there were no real moments of concern in the second half as the hosts effectively shut down their beleaguered opponents.
As Hearts committed more men forward to little effect, Stephen Robinson's side were switched on at the back and had license to roam but could not find a killer third goal.
St Mirren had been slow to start and struggled for fluency from open play before the interval but made their physicality pay against a side low on confidence.
Olusanya's sixth goal of the season was an emphatic strike and he leads the line with impressive energy to set the tone for a hard-grafting side.
Shankland toils as Hearts 'fizzle out'
Hearts had made life difficult for Celtic last time out and began brightly, with Spittal twice threatening in the opening moments and Beni Baningime neat and tidy in the middle of the park.
But heads went down once the second St Mirren goal went in and travelling fans vented their fury at full-time.
A James Penrice crack from distance was the only shot home goalkeeper Ellery Balcombe had to deal with.
Lawrence Shankland, so prolific last term, has yet to find the net this season - the longest barren run of his Hearts career.
The striker did lay on a clever cross for Spittal to head over but there was no service coming the other way and his frustration was clear in a second half when Hearts completely lost their way, with Naismith admitting his team had "fizzled out with a whimper".
What they said
St Mirren's defensive display pleases Robinson
Hearts manager Steven Naismith: "Two set-plays have cost us and then in the final third we weren't clinical enough.
"It's split second decisions – it's not getting the better of your one-on-one duels. We were the better team for 60-65 minutes but you need to get something from that."
St Mirren manager Stephen Robinson: "If you're hard to break down, which I think we were today, you're going to score goals.
"We're three unbeaten now and that's a really good start to the season for us considering the run we've had and the teams we've played."
'I'm definitely up for the fight' - Naismith
