Motherwell won at Celtic Park for the first time in nearly eight years, coming from behind to do so.
Louis Moult's double turned the game around after Nir Bitton's deflected shot had given the champions the lead.
It means Celtic have failed to win at home in their last four games, the first time that has happened since Tony Mowbray was manager.
They remain a point clear of Aberdeen at the top of the league, while Well's revival under Mark McGhee continues.
The match was prefaced by an emotional unveiling of a statue of Celtic's legendary European Cup-winning captain, Billy McNeill.
The thousands of supporters who gathered for the occasion would have been underwhelmed by what unfolded inside the stadium in the opening 45 minutes.
Their team dominated possession but found Motherwell to be well organised and therefore difficult to penetrate.
But the chess-like approach to the first half could not have been in greater contrast to the action-packed second period.
Lionel Ainsworth should have put Motherwell ahead, but his chip over goalkeeper Craig Gordon also cleared the crossbar.
It looked like Motherwell would pay a hefty price for that as Tom Rogic burst clear, squared for Bitton and the midfielder's shot took a big deflection off Keith Lasley on its way past goalkeeper Connor Ripley.
However, Marvin Johnson, whose pace had already caused Celtic problems, soon fired the ball across goal for Moult to tap into the net.
And the game was turned on its head when Scott McDonald's sharp turn enticed Jozo Simunovic into a rash challenge.
It gave Moult the opportunity to double his and Motherwell's tally, which he duly took, rolling the penalty straight down the middle as Gordon dived to his left.
They could have gone further ahead but for Gordon, who rushed off his line to block from McDonald after Dedryck Boyata got into trouble and then used his left foot to deny Moult a hat-trick.
In between those efforts, Bitton had a shot blocked on the line and Ripley saved from Scott Allan and Kris Commons.
Celtic piled forward in the closing stages but failed to create any further openings as Motherwell celebrated a hard-earned victory.
Full Time Match ends, Celtic 1, Motherwell 2.
90:00 +4:24 Full timeFull Time Second Half ends, Celtic 1, Motherwell 2.
90:00 +4:04Corner, Celtic. Conceded by Luke Watt.
90:00 +3:07Callum McGregor (Celtic) wins a free kick in the defensive half.
90:00 +3:07Foul by Marvin Johnson (Motherwell).
90:00 +2:27Attempt blocked. Kris Commons (Celtic) right footed shot from outside the box is blocked.
89:00Kieran Tierney (Celtic) wins a free kick in the attacking half.
88:59Foul by Louis Moult (Motherwell).
85:04Attempt saved. Kris Commons (Celtic) left footed shot from outside the box is saved in the centre of the goal.
84:32Scott Allan (Celtic) wins a free kick in the defensive half.
84:32Foul by Keith Lasley (Motherwell).
83:55Foul by Nadir Ciftci (Celtic).
83:55Ben Hall (Motherwell) wins a free kick in the defensive half.
83:08Attempt missed. Jozo Simunovic (Celtic) right footed shot from outside the box misses to the right.
80:10 SubstitutionSubstitution Substitution, Motherwell. Luke Watt replaces Lionel Ainsworth.
79:17Attempt saved. Marvin Johnson (Motherwell) right footed shot from the centre of the box is saved in the centre of the goal.
78:31Corner, Celtic. Conceded by Connor Ripley.
78:22Attempt saved. Kris Commons (Celtic) right footed shot from outside the box is saved in the top right corner.
77:27 BookingBooking Nir Bitton (Celtic) is shown the yellow card for a bad foul.
77:23Foul by Nir Bitton (Celtic).
Scott McDonald (Motherwell) wins a free kick in the attacking half.
76:25 SubstitutionSubstitution Substitution, Motherwell. Louis Laing replaces Stephen McManus because of an injury.
76:10Attempt missed. Nir Bitton (Celtic) right footed shot from outside the box is high and wide to the right.
75:41Delay over. They are ready to continue.
74:53Delay in match Stephen McManus (Motherwell) because of an injury.
73:46 SubstitutionSubstitution Substitution, Celtic. Carlton Cole replaces Tomas Rogic.
73:26Attempt missed. Lionel Ainsworth (Motherwell) left footed shot from outside the box is just a bit too high from a direct free kick.
72:40Foul by Mikael Lustig (Celtic).
72:40Scott McDonald (Motherwell) wins a free kick in the defensive half.
71:58Attempt saved. Scott Allan (Celtic) header from the left side of the six yard box is saved in the top centre of the goal.
71:32Attempt blocked. Nir Bitton (Celtic) left footed shot from the right side of the six yard box is blocked.
71:14Corner, Celtic. Conceded by Marvin Johnson.
66:57 SubstitutionSubstitution Substitution, Celtic. Scott Allan replaces James Forrest.
64:25Attempt missed. Louis Moult (Motherwell) right footed shot from the centre of the box is too high.
64:16Attempt saved. Scott McDonald (Motherwell) right footed shot from the centre of the box is saved in the bottom right corner.
62:42Nir Bitton (Celtic) wins a free kick in the attacking half.
62:42Foul by Keith Lasley (Motherwell).
62:16Attempt missed. Stephen McManus (Motherwell) header from a difficult angle on the right misses to the right.
61:51Corner, Motherwell. Conceded by Dedryck Boyata.
61:06Corner, Motherwell. Conceded by Kieran Tierney.
60:28Corner, Motherwell. Conceded by Nir Bitton.
59:42Dedryck Boyata (Celtic) wins a free kick in the defensive half.
59:42Foul by Scott McDonald (Motherwell).
58:41 Goal scoredGoal! Goal! Celtic 1, Motherwell 2. Louis Moult (Motherwell) converts the penalty with a right footed shot to the bottom left corner.
58:01Penalty conceded by Jozo Simunovic (Celtic) after a foul in the penalty area.
58:01Penalty Motherwell. Scott McDonald draws a foul in the penalty area.
56:13Dedryck Boyata (Celtic) wins a free kick in the attacking half.
56:13Foul by Scott McDonald (Motherwell).
55:29Kieran Tierney (Celtic) wins a free kick in the attacking half.
55:29Foul by Scott McDonald (Motherwell).
54:32Hand ball by Scott McDonald (Motherwell).
54:19Attempt blocked. Kris Commons (Celtic) right footed shot from outside the box is blocked.
53:35James Forrest (Celtic) wins a free kick in the defensive half.
53:35Foul by Ben Hall (Motherwell).
52:11 Goal scoredGoal! Goal! Celtic 1, Motherwell 1. Louis Moult (Motherwell) right footed shot from the right side of the six yard box to the top right corner. Assisted by Marvin Johnson.
50:57Attempt missed. Tomas Rogic (Celtic) left footed shot from outside the box is close, but misses to the left.
50:30Attempt blocked. James Forrest (Celtic) right footed shot from the left side of the box is blocked.
48:24 Goal scoredGoal! Goal! Celtic 1, Motherwell 0. Nir Bitton (Celtic) left footed shot from the centre of the box to the bottom left corner. Assisted by Tomas Rogic.
47:33Attempt missed. Lionel Ainsworth (Motherwell) right footed shot from the centre of the box is just a bit too high.
46:55Corner, Celtic. Conceded by Lionel Ainsworth.
46:46Attempt blocked. James Forrest (Celtic) right footed shot from long range on the left is blocked.
45:51Attempt saved. James Forrest (Celtic) header from the left side of the six yard box is saved in the top centre of the goal.
45:34Corner, Celtic. Conceded by Scott McDonald.
45:00Second Half begins Celtic 0, Motherwell 0.
45:00 SubstitutionSubstitution Substitution, Motherwell. Lionel Ainsworth replaces Liam Grimshaw.
45:00 +1:09 Half timeHalf Time First Half ends, Celtic 0, Motherwell 0.
45:00 +0:33Foul by Nir Bitton (Celtic).
45:00 +0:33Scott McDonald (Motherwell) wins a free kick in the defensive half.
44:20Foul by Kris Commons (Celtic).
44:20Keith Lasley (Motherwell) wins a free kick in the attacking half.
43:40Dedryck Boyata (Celtic) wins a free kick in the attacking half.
43:40Foul by Louis Moult (Motherwell).
43:00Attempt missed. Jozo Simunovic (Celtic) header from the centre of the box is close, but misses to the left.
42:37Mikael Lustig (Celtic) wins a free kick in the defensive half.
42:37Foul by Marvin Johnson (Motherwell).
41:39Kieran Tierney (Celtic) wins a free kick on the right wing.
41:39Foul by Scott McDonald (Motherwell).
40:43Attempt missed. Callum McGregor (Celtic) left footed shot from outside the box is too high.
37:05Foul by Scott McDonald (Motherwell).
37:05Kieran Tierney (Celtic) wins a free kick in the attacking half.
36:08Attempt missed. Nadir Ciftci (Celtic) right footed shot from a difficult angle on the right is close, but misses to the left.
32:19Attempt missed. Kris Commons (Celtic) left footed shot from the right side of the box is close, but misses to the left.
29:01Foul by Louis Moult (Motherwell).
29:01Mikael Lustig (Celtic) wins a free kick on the right wing.
27:21Attempt missed. Kieran Tierney (Celtic) left footed shot from outside the box misses to the left.
25:43Foul by Ben Hall (Motherwell).
25:43Tomas Rogic (Celtic) wins a free kick in the defensive half.
22:57Attempt blocked. Nadir Ciftci (Celtic) right footed shot from outside the box is blocked.
21:11Stephen Pearson (Motherwell) wins a free kick in the attacking half.
21:11Foul by Tomas Rogic (Celtic).
18:59Attempt saved. Nir Bitton (Celtic) right footed shot from the centre of the box is saved in the top right corner.
14:34Corner, Celtic. Conceded by Josh Law.
11:59Corner, Motherwell. Conceded by Dedryck Boyata.
10:36Attempt missed. Nir Bitton (Celtic) left footed shot from outside the box is just a bit too high from a direct free kick.
9:30Foul by Stephen McManus (Motherwell).
9:30Kris Commons (Celtic) wins a free kick in the defensive half.
3:10Attempt missed. Callum McGregor (Celtic) right footed shot from outside the box is close, but misses the top right corner.
0:00First Half begins.
0:00Lineups are announced and players are warming up.
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