Celtic manager Ronny Deila bemoaned his side`s lack of fight as they slipped to a shock 1-0 defeat to St Johnstone at Celtic Park on Wednesday.
The defending champions headed in to their rearranged fixture hoping to open a formidable nine-point gap over Aberdeen - who they thrashed 4-0 on Sunday - at the top of the table.
But following a bright start it was St Johnstone who grabbed the only goal of the match in the 54th minute thanks to a sumptuous Danny Swanson strike from 25 yards.
It was Celtic`s first domestic defeat of 2015 and ended their run of eight straight victories in the league.
Deila refused to blame Celtic`s gruelling schedule, which has seen them play three games in six days, for the defeat and insisted his side should have performed better.
"Today we had a lack of fight. We just didn`t fight enough," Delia said.
"We want to win and we realise every time we play in Scotland we are favourites and we should win.
"We have played three games in a very short time and one of those was in Italy. I feel for the boys and I understand it is very tough. But it is disappointing that we lost and didn`t get anything from the game.
"We started the game quite well, got a number of chances but didn`t score. In the end we got too open and didn`t press as a team. Offensively we can`t play through the centre of the park all the time and we have to get much more width in the team and not be too easy to read.
"It is a little bit like the feeling I had when we lost against Hamilton, although we created more chances in that match than tonight.
"It`s not about finding excuses. The performance was not good enough. There were some tired players out there, but we should be better as a unit."
The Hoops now have two weeks off league duty as they prepare to take on Dundee United at Tannadice in Sunday`s Scottish Cup quarter-final before facing the same side at Hampden the following week in the League Cup final.
And Deila has challenged his side to channel their disappointment at suffering their first home defeat since October into continuing their quest of claiming a historic domestic treble.
"Today we got a big set-back. I`m disappointed but that can happen with teams and we have to bounce back on Sunday so we can make this into something positive in the end," the Celtic manager said.
"We have to move on. We have to learn from this and make ourselves ready for Sunday.
"We have four days to get ready and we are going to make a good performance against Dundee United.
"The only way we can make this good again is to win on Sunday."
St Johnstone manager Tommy Wright was delighted with the victory that pushes the Perth side back into the top six.
"We asked them to be brave in possession and they were. When you come here you`ve got to try and keep the ball and we did that. That gave us the platform to go and win it," Wright said.
"The goal was worthy of winning any game. It was a tremendous strike.
"I can`t remember any real clear cut for Celtic and overall I don`t think anyone can suggest we didn`t deserve the victory."