Hearts head coach Robbie Neilson said defensive errors meant his side lost their four-match unbeaten run.
Neilson's side were comprehensively beaten 3-0 by St Johnstone at Tynecastle, with Murray Davidson scoring twice from corners.
"We just didn't get ourselves going in the game," Neilson told BBC Scotland.
"We had four clean sheets in a row and we're looking good defensively but we lose two really bad goals from set plays which is disappointing."
The head coach felt the performance was a rare blip in an otherwise impressive Premiership campaign thus far.
Neilson brought on Sam Nicholson and Jamie Walker in the second half, in an attempt to inject some attacking incision, but Hearts created little.
Darnell Fisher scored a late third as the hosts were caught on the counterattack.
"We tried to change the formation and the personnel to try and give us a lift," he said. "But we just couldn't get that final pass.
"We had a lot of possession but we weren't delivering the ball into the box. I just felt it was a poor performance but we haven't had many this season."
Saints boss Tommy Wright said the win was the perfect tonic after missing the midweek draw with Ross County with a stomach bug.
Wright feels his players are now approaching the type of form they showed earlier in the season.
"We are back on track," he said. "There is a lot of criticism given out, even from our own quarters, but I tend just to look at the next game.
"I know the squad of players I have got and I think know where we could be at the end of the season."
|St Johnstone - last five league finishes|
The win lifts St Johnstone into fourth place in the table but Wright says there is still work to be done to secure their top-six status for the season run-in.
"I think maybe Hamilton dropped out of it today [losing to Partick Thistle]," said the manager.
"While 42 or 43 points normally gets you in, at the moment it doesn't, so we have to make sure in our next two games we do enough. With performances like that we should be okay."