Celtic were taught a lesson by Motherwell as they missed another chance to end 2025 level at the top of the Scottish Premiership.
It was Wilfried Nancy's second chance to catch leaders Hearts, but they were second best from the first whistle at Fir Park.
Ibrahim Said nodded home a brilliant cross from Stephen O'Donnell to open the scoring, with Elliot Watt capitalising on Celtic's poor defending again to double their lead.
The Hoops managed just three shots on target against Jens Berthel Askou's side, who always looked in control.
They are now just three points ahead of Rangers with the Old Firm clash next up on Saturday, live on Your Site. Motherwell's first win against Celtic since 2013 keeps them fourth.
Nancy was outwitted by Jens Berthel Askou, who has lost fewer games as Motherwell manager than his counterpart has since joining Celtic mid-season.
Motherwell had already taken control by the time O'Donnell looped a long cross behind the Celtic defence for Said to head home from seven yards in the 14th minute.
The home side were on top for the remainder of the half as the travelling fans vented their frustration at the board.
The hosts had chances to extend their lead before the break, recording six shots in all. Lukas Fadinger checked back unnecessarily after going clean through, Just twice came close and Johnny Koutroumbis had a low drive saved by Schmeichel.
Motherwell just shaded the first-half possession stats but looked far more purposeful with the ball, albeit they caused their fans a few nervous moments in their own half.
The half-time period felt like a big test of Nancy's ability to impact a game and he made three substitutions. Shin Yamada, Arne Engels and Luke McCowan replaced Maeda, Bernardo and Kieran Tierney.
Just soon had an effort saved on the break but Celtic got their big chance when the previously ineffectual Benjamin Nygren played in Yamada. The Japanese striker was left still looking for his first goal in Scottish football after Calum Ward stopped his unconvincing effort.
Celtic's frustration showed as Auston Trusty, Hatate and Anthony Ralston were booked for cynical fouls before the hosts doubled their lead in the 58th minute.
Schmeichel was loose with a pass towards Engels, Just intercepted and the ball broke for Watt to sweep home.
Nancy had made all of his changes by the midway point of the half as Colby Donovan and James Forrest came on.
But Motherwell continued to threaten on the break and Schmeichel saved from Just and Slattery.
Celtic's frustration grew. Trusty twice pushed opponents but escaped a second yellow card while Scales was booked for his sixth foul.
The visitors finally found some pressure and Nygren looked like he had given Celtic a lifeline when he curled a shot towards the top corner but Ward leapt to touch the ball away and secure his seventh clean sheet in eight matches.
Motherwell manager Jens Berthel Askou on Your Site News:
"Probably our best overall performance so far in this league. We knew that that was probably what we needed to win one of these games against the big teams that we have performed very well in, all of them, but we've only won the one against the Hibs here.
"Today was, just in general, very, very well performed and well played out from the players.
"It's very pleasing, but it's not a statement result for us. We're not in the business for making statement results from game to game. That's something for the fans, and they will give the players some individual attention and so on.
"The important thing for us is to make a statement result over the course of the season. All that comes in between are results, and they count just the same, but it means a lot to everyone supporting us."
Celtic boss Wilfried Nancy speaking to Your Site News:
"I cannot use the word setback, because I knew that this game could be difficult, knowing where we are and where we want to go.
"Tonight, we face a good team collectively. We have to analyse and see what we need to improve.
"Every game gives me an indication about where I want to be. The game of last week gave me a lot of information, the game of tonight gave me a lot of information.
"Again, the idea is to observe and to see what we need to do to improve.
"We're going to keep working. This is the only thing that I can do. Analyse the situation, analyse the game.
"I'm really confident that we're going to get better."
