Celtic's march towards the title was slowed by James McFadden at Fir Park as Motherwell closed to within 19 points of the leaders.
McFadden celebrated his first Motherwell start for 10 years by helping Stuart McCall's men to victory – and second place in the table – over Neil Lennon's side.
The 29-year-old made his name in a 2-1 victory over Celtic back in September 2002 when he scored and tormented Martin O'Neill's side.
Michael Higdon volleyed the winner in the 73rd minute as Motherwell beat Celtic for the first time in exactly two years.
Chris Humphrey had opened the scoring prior to the break, before Georgios Samaras headed an equaliser for the visitors.
McFadden had come off the bench twice since re-signing, appearing in consecutive defeats against Dundee United and Ross County which had seen 'Well slump from second to fourth place.
But his first start since playing for Everton against Wolves on May 6 last year saw them return to second spot.
His lack of game time meant he was never going to be running at Celtic all night but his skill, improved football brain and willingness to work helped Motherwell boost their hopes of qualifying for Europe.
Goals looked on the cards when the team sheets arrived with both sides lining up with attacking 4-4-2 formations, with McFadden and Humphrey on the flanks for Well and Kris Commons and James Forrest the wide men for Celtic.
Stevie Hammell recovered from injury to join McFadden and Keith Lasley as survivors from that 2002 victory while visiting boss Neil Lennon made five changes ahead of Celtic's cup ties against St Mirren and Juventus with Adam Matthews, Tomas Rogic, Victor Wanyama, Commons and Samaras all coming in.
Anthony Stokes had Celtic's first chance on the break but he mis-kicked an attempted volley following Forrest's cross.
The game remained finely poised and Motherwell took the lead in the 31st minute. The goal originated from Darren Randolph's goal-kick with McFadden heading the ball on for Henrik Ojamaa to put Celtic on the back foot.
Ojamaa laid it off to Lasley who threaded the ball into the path of the onrushing Law. The midfielder turned centre-back Wanyama inside and out before aiming a shot to the far corner.
The effort beat Forster but would have gone wide had Humphrey, who was level with Emilio Izaguirre when Law shot, not run in and finished off at the back post from close range.
An object appeared to be thrown from the Motherwell fans in the East Stand while Commons was waiting for Efe Ambrose to come on for Kayal before taking a throw.
Celtic soon silenced the home support with a goal from nothing in the 63rd minute. Forrest made space to cross on the right and Samaras seemed to catch out Randolph as he raced in to head inside the near post as the keeper came off his line to anticipate the ball dropping into his hands.
Ambrose and Matthews got in each other's way on 73 minutes at a high ball in the right-back position and Law broke down the left again following Ojamaa's pass.
Law turned Ambrose and stood up a left-footed cross to the back post where Higdon arrived to cushion a volley into the roof of the net to seal all three points.