Wilfried Nancy’s first match in charge of Celtic ended in disappointment as Hearts left Glasgow with a 2–1 victory, opening a three-point gap at the top of the Scottish Premiership.
Claudio Braga stunned the home crowd midway through the first half when he stripped Callum McGregor and calmly slotted home.
Celtic players immediately appealed for offside, but replays confirmed Arne Engels had kept Braga onside in the initial phase.
The visitors doubled their lead soon after the break.
Oisin McEntee powered in a header from Harry Milne’s corner, though the set piece itself was awarded despite a marginal offside shout involving Lawrence Shankland.
Hearts continued to threaten on the counter, and Engels was denied a third by a sensational stop from Alexander Schwolow.
Moments later at the opposite end, Reo Hatate rattled the bar with a first-time volley.
Celtic finally broke through deep into stoppage time when Kieran Tierney smashed in from close range, but the hosts ran out of time to complete the comeback.
Nancy’s side remain in touching distance, with both Celtic and Rangers holding a game in hand. Motherwell and Rangers sit six points behind Celtic following their weekend wins.
Throughout the closing stages, Nancy reshuffled his team repeatedly, pushing more attackers into advanced positions while barking instructions at McGregor.
Hearts, however, grew stronger as the game progressed - winning duels, disrupting Celtic’s rhythm, and counter-attacking with intent.
The victory marks their second league win over Celtic this season.
Nancy opted for a 3-4-3 reminiscent of his Columbus Crew blueprint, moving away from the back-four setups of O’Neill, Rodgers, and Postecoglou.
Trusty, Scales and Tierney formed the last defensive line, with Yang Hyun-Jun and Tounekti operating as wing-backs. Hatate and Nygren supported Daizen Maeda up front.
The shape allowed Celtic to press aggressively early on, but they lacked the decisive final pass in the first half. Even after the break, their attempts rarely troubled Schwolow until Tierney’s late strike.
It’s worth noting that injured regulars such as Carter-Vickers, Johnston and Jota may adapt more naturally to Nancy’s preferred structure once they return.
BBC pundit Ryan Stevenson warned that Hearts needed to exploit the space behind Celtic’s reworked defensive line.
They managed exactly that - Milne’s cross nearly found Shankland before Braga’s opener arrived from a sequence of errors: Kyziridis’ header forward, Trusty’s clearance, Milne’s mis-hit, and McGregor losing out to Braga.
Although Hearts initially expected a flag, VAR confirmed the goal as Engels played Braga onside.
McEntee’s header for the second came from another moment of slack defending, with the Hearts man showing more hunger in the box.
As Stevenson put it: “Hearts simply wanted it more - they outfought Celtic today.”
Celtic manager Wilfried Nancy: "This is not about the system. We started one way in the first half and the second half, we kept going and towards the end, it was not the same system.
"This is more about to check if we play with personality, to check what we can do better to unbalance the low block, what can we do better to avoid the two goals that we conceded? We had really good moments and we had moments we have to improve on.
"We conceded the goal but to be honest, I felt that it didn't change the attitude of the players. We pushed a little bit more but we conceded the second goal and after that we started to rush. We put a lot of crosses inside the box knowing that they are so big. We could've been a little bit better to combine and attack a different way.
"I was pleased with the mentality. The performance was really interesting. Defensively, we were really good but we missed the few opportunities."
Hearts manager Derek McInnes: "We wanted a positive result. On the day, we had to do a lot right. There was loads that I liked about my team. You've got to think as if you've won the game before you've won and carry yourself that way and I thought we did that.
"We had something to hang on to after Claudio's goal just before half-time I thought we deserved at the moment. Oisin gets the second goal. We defended well, we adapted to Celtic throwing two strikers on and trying to put four on our last line.
"We turned to a five. We defended the box brilliantly apart from two moments, when Engels hits off the bar and the goal from Kieran Tierney.
"We're well into December now. The players shouldn't doubt themselves, shouldn't doubt what we are. Once we come out the second round of fixtures, you've got a rough idea of where you are. To beat Celtic home and away takes a lot of doing. Hopefully, we can keep winning games."
