Leaders Hearts fought back twice to earn a 2-2 draw with 10-man Celtic in a thrilling Scottish Premiership encounter.
It was billed as the biggest game of the season so far and it lived up to the hype as Benjamin Nygren curled home a free-kick to give the Hoops an early lead.
Stuart Findlay headed in an equaliser after missed chances from Alex Kyziridis, but Hyun-Jun Yang tapped in a brilliant ball from new signing Tomas Cvancara to restore Celtic's lead.
Hoops defender Auston Trusty was sent off following a VAR review for a last-ditch challenge before Claudio Braga smashed the ball in from another set-piece to level again for Hearts.
Rangers' 3-0 win against Dundee means Hearts are now four points clear at the top with Celtic dropping to third, two points behind their Old Firm rivals.
The visitors got off to the perfect start when Nygren curled a superb free-kick beyond the left hand of Gordon from 20 yards in the seventh minute. It was the first time the Parkhead side had scored direct from a free-kick since 2021.
Home manager Derek McInnes stormed towards the Celtic technical area, visibly angered by the nature of the celebrations from a member of the Hoops' backroom staff.
Hearts responded well and Braga and Kyziridis had golden chances to equalise but were denied by Kasper Schmeichel as the Edinburgh side enjoyed the majority of the first-half pressure.
The hosts continued on the front foot after the break and equalised within three minutes of the restart when Findlay met Leonard's corner at the back post and nodded down into the net.
Hearts looked set to go ahead in the 54th minute when Kyziridis got himself free in the box but Liam Scales got back to make a brilliant goal-saving challenge.
Celtic had offered little as an attacking force since their early goal but served a reminder of their threat when Cvancara sent a looping header against the woodwork on the hour.
And the champions duly restored their lead two minutes later when Cvancara burst away down the left and rolled a tantalising delivery across the face of goal for the in-rushing Yang, who rammed home from a couple of yards.
Moments after Kieran Tierney limped off injured, Celtic were reduced to 10 men for the second game running when Trusty was adjudged, following a VAR check, to have denied a goalscoring opportunity by fouling Pierre Landry Kabore as he tried to get on the end of a through ball.
Hearts made the extra man count in the 87th minute when Braga thumped home from eight yards after substitute Oisin McEntee had headed Harry Milne's free-kick down to him.
Hearts head coach Derek McInnes on Your Site:
"I thought the attitude of the team was terrific throughout. You want your team to never give up.
"The technique for their first goal was terrific. Sometimes you just have to admire a top-class finish.
"We had it all to do. Celtic have so many good players. We just needed to show a wee bit of calmness. Missed opportunities, we should've been doing better.
"If we kept it one each for longer, we should win the game. We had more clear-cut chances, more shots, more pressure.
"I think that the fact that we are disappointed not to win the game says a lot.
"To come back against Celtic, you need to do a lot right, but underneath that is character and belief. I thought that was screaming out of the players.
"We've been top of the league for four months - that's not just a purple patch.
"We don't really care about Rangers or Celtic - we need to take each game as it comes."
Celtic manager Martin O'Neill speaking to Your Site:
"It was a very tough match. We have done pretty well. Splendid second goal by us.
"The controversial moment, I must admit, was the red card.
"It's no more a red card than a blue card [a proposed 10-minute sin-bin]!
"First of all, the ball was going away from goal, second of all, we had a player covering. As far as I remember, if you're going away from goal, it's not a red card.
"I'm not sure that either team had control. We were under pressure, away from home at the league leaders. But after we score the second we were back in control.
"The sending off had a major effect, psychologically and physically.
"We're still in the competition. Simple as that. We've given ourselves ground to catch up from, but we're still there.
"We have to try to get a result on Thursday night. There's terrific spirit in the side, and that'll be very important come the end of the season."
