Hearts manager Daniel Stendel admitted his team lacked fight during their 1-0 defeat against relegation rivals St Mirren.
Hearts were looking to leapfrog the Buddies but ended the night four points adrift at the foot of the Ladbrokes Premiership with the home team opening up a six-point gap.
Saints looked the more determined team from the off and took a deserved lead in the 49th minute when Jon Obika finished following Ross Wallace's long pass.
Hearts eventually pushed the Buddies back but could not seriously trouble goalkeeper Vaclav Hladky at any stage.
Stendel said: "From the first minute we're not ready for this game. St Mirren played as we expected and we didn't have everybody ready to take the fight and win this duel. That was the biggest disappointment.
"The goal we conceded was more our fault than a great chance and it decided the game."
When asked why the players did not seem ready for such an important game, he said: "I cannot understand – I have no reasons for this. Especially after last week and our results. There are no reasons for a performance like this.
"I expected it to be a little bit different but no one in our team expected a performance like this in the first half.
"I said to the players it's not decisive but it's a big blow.
"I can say I never give up and I expected this from my players but we cannot play like this. It doesn't matter if we lose or win, we cannot play with so little fight for our position in the league and our club. It wasn't enough in the first half."
Saints manager Jim Goodwin hailed his players for their approach.
"Sometimes managers get credits for tactics, formations or changes they make during the game but I can take no credit for that," he said.
"That was a performance that the players deserve all the plaudits for. It was a performance of sheer attitude, character, desire, resilience, everything that you want from a group of players.
"It's a big night for the club, the biggest game of the season. It was massive we didn't lose. In my own head I wanted to make sure we kept the gap at three at least so I didn't think we needed to go gung-ho, it was more of a must-win for Hearts.
"But the fact we extended the gap to six points is a huge relief."
The win came at a cost with three players going off injured for the hosts.
"Conor McCarthy looks as if he's done his hamstring so a couple of weeks is probably best-case scenario," Goodwin said.
"Ilkay Durmus felt his groin a little bit so hopefully we have caught that early enough and Cammy MacPherson took a bad bang in his thigh. Saturday might come too early for him."