Danny Johnson arrowed a late equaliser for Motherwell to prevent Celtic going back to the top of the Ladbrokes Premiership.
Celtic paid the price for failing to build on Ryan Christie's 13th-minute opener as their dominance in possession at Fir Park counted for nothing, and they were left to rue a first-half penalty miss by Leigh Griffiths.
The champions were heading back to the top of the table three days after Rangers leapfrogged them but Johnson's 88th-minute strike ensured Kilmarnock travel to Parkhead on Saturday as leaders following Aberdeen's 1-0 win at Ibrox.
Motherwell had suffered a hugely disrupted start to proceedings. Both sides made a number of changes – four for Motherwell and seven for the visitors, who handed Jonny Hayes and Cristian Gamboa starts, but the hosts were forced into two more early on as defenders Peter Hartley and Liam Donnelly both went off injured.
The first switch forced them to move to a flat back four as midfielder Andy Rose came on and the second left them vulnerable down the right of their defence.
Celtic took full advantage with Motherwell still preparing a substitution and Christie ran on to Kieran Tierney's inside pass before guiding the ball into the far corner with the outside of his foot to net his sixth goal in nine matches and follow his Betfred Cup winner on Sunday.
Adam Livingstone came on at left-back before the game restarted and Celtic soon had the ball in the net again, but Filip Benkovic was penalised for a tug on Tom Aldred before netting from a deep corner.
David Turnbull shot just over from 18 yards for the hosts but Celtic were dominating possession and had a great chance to double their lead in the 41st minute after Rose's clumsy challenge on Christie. But Mark Gillespie dived to stop Griffiths' penalty and punched the loose ball to safety.
Scott Sinclair replaced Olivier Ntcham at half-time and both he and Hayes saw shots blocked in a goalmouth scramble.
Griffiths went off midway through the half after receiving treatment, although his number was already up as the physio ran on.
Livingstone soon became the third Motherwell defender to succumb to injury and Stephen Robinson decided to go for broke by putting on striker Curtis Main.
Celtic continued to look as comfortable as the scoreline could allow but they had a warning in the 82nd minute when substitute Odsonne Edouard gifted Conor Sammon the ball. The striker drove well at the Celtic defence but Craig Gordon saved well.
An equaliser still looked unlikely but Johnson made the most of a half-chance after the ball broke to him just inside the left edge of the box and drilled the ball just inside the far post.
