Hearts boss Craig Levein was left frustrated after watching his team dominate possession against Kilmarnock but lose 1-0.
Ross Millen netted a second-half goal to secure the three points for the Rugby Park side, with the top four in the Ladbrokes Premiership separated by three points.
It is was only Hearts' second defeat at Tynecastle in 18 months - dating back to a 2-1 defeat to Aberdeen in May 2017.
"I have got to be mindful that we have had a difficult period," Levein said. "We can't continue to go through the league season winning every match so that's a reality check for us.
"We haven't lost here in a long time... it leaves a bitter taste. It is important we get back on the saddle once the international break's out the road and we're ready to go."
Levein called on some of his players to step up in the absence of key players such as Steven Naismith and Uche Ikpeazu.
He said: "There's loads of way losing a match but that's most frustrating. Possession, dominating the play but we should have been better in the final third. To lose that way makes me feel really frustrating.
"We had a lot of good football and a lot of opportunities but we did get frustrated. Instead of being patient with our switches of play and probe down the sides or give our full-backs time to put crosses into the box we didn't do that well enough.
"Players who we have got out injured, I think it is easier to score goals with them in the team and everybody knows that but at the same time we need people to step up at times like this to put the ball in the back of the net and sometimes that's not just strikers or attacking midfielders, we had opportunities for our centre-backs today as well to score."