Celtic manager Neil Lennon lamented his team's display as their 3-2 defeat at Inverness tilted the Scottish Premier League title race in Rangers' favour.
"Defensively we were poor, going forward we were poor. You never expect that kind of performance," Lennon told BBC Scotland.
"We need to take the title to at least the last day of the season.
"And with a but of luck somebody might do us a favour along the way."
The defeat for Celtic against the bottom-six side leaves them a point behind table-toppers Rangers, with both teams having three games left to play.
Celtic face trips to Kilmarnock and Hearts, then finish up against Motherwell at home, while Rangers have home games against Hearts and Dundee United, before travelling to Kilmarnock on the final day.
Adam Rooney gave Inverness the lead on Wednesday, before Kris Commons quickly levelled for Celtic to leave the score level at the break.
But Inverness raced into a 3-1 lead thanks to fine strikes from Grant Munro and Shane Sutherland, with Commons scoring a penalty in added time.
"We didn't start the second half anywhere near the way we should have," said Lennon.
"At half-time we told them we needed a bit more in the final third. We kept getting into good positions and failing.
"Defensively some of the guys picked today of all days to have their worst game of the season. We went AWOL at the start of the second period.
"Midfield were okay, but our front two in the second half gave us very, very little. They never looked like scoring.
"I'm very disappointed with the second-half performance. Very disappointed."
The Celtic boss added that his team did not look like a team who were looking to take a two-point lead in the championship.
"We looked like a team that ran out of ideas very quickly - and ran out of a bit of heart as well.
"That's not something I can't throw at them for the majority of the season. Inverness wanted it more.
"It could have been worse. We were all over the place - particularly in the central areas.
"The two centre-halves had just one player to mark, but Rooney kept running away from us."
The Celtic boss appeared irate on the sidelines at 3-2 when referee Stevie O'Reilly waved away claims for a second spot-kick when Pat McCourt tumbled in the box when challenged by Munro.
"It was a shout, but I'm not so sure. I'd need to see it again," conceded Lennon.
"I thought that earlier when [Shaun] Maloney was brought down by the goalkeeper was probably a better shout than Paddy's one.
"The penalty that we scored near the end gave us a little bit of hope but we didn't do enough."
Meanwhile, Celtic's Israeli midfielder Beram Kayal could face some time out of the team after being carried off on a stretcher in the second half.
"Kayal is in trouble," said Lennon. "He has a touch of concussion and he looks as though he might have a broken wrist as well."