Manager Gary Locke has urged his Hearts players not to "feel sorry" for themselves after slipping 10 points adrift at the bottom of the table.
Hearts, who began the season with a 15-point penalty after the club entered administration, ahead of the international break.
"Unfortunately, we didn't take our chances," said Locke.
"We've just got to raise the spirits of the players and hopefully we can get back on track in a fortnight's time."
John McGinn and Paul McGowan were on target in St Mirren's victory and Locke admitted his team struggled to "get going".
"We had a couple of moments of slackness which gave them a wee lift," he explained.
"We still had chances even at 1-0 down. Callum Paterson's hit one over the bar. If that goes in, it's an absolutely different atmosphere around the stadium.
"With him missing that and them going right up the park and scoring the second goal, it deflates everyone.
"The boys have done great so far this season. It's a set-back for us, there's no doubt about but one thing we can't do, we can't feel sorry for ourselves. We've just got to pick the heads up.
"It's a bad day at the office but we need to move.
"It was never going to be easy. We had a reasonable start to the season and recently we've not picked up the results that we need but we'll still keep going. I'll certainly not give up."