Match summary
The dominant Edinburgh side powered eight points clear of their Glasgow rivals at the summit of the Scottish Premiership to bolster their early-season championship claims and deepen the malaise around Brendan Rodgers' side.
Alexandros Kyziridis' fine strike and Lawrence Shankland's penalty gave Derek McInnes' side a two-goal advantage that the reigning champions could not recover from.
The young defender - one of three youngsters in the Celtic starting lineup - scored an own goal in the early stages to put the home side ahead at a energetic their home ground, and it was the youngster's infringement that led to the penalty.
A stylish finish from McGregor of the season had swiftly equalized Hearts' opener, and the Swedish attacker almost put Celtic in front, choosing placement over power and allowing Alexander Schwolow to make a crucial stop.
But Derek McInnes' irrepressible Hearts regained dominance to hand Celtic to back-to-back losses for the first time since 2023.
It also gives the Edinburgh side a significant lead at the top of the table.
The last time they were this far ahead was in the 2005-2006 season under George Burley, when they ended as runners-up - one of just four occasions that a team has failed to win the title having held such a lead in the past 27 years.
McInnes, whose former team were second to Celtic on multiple times, has been working hard to downplay title talk, as Hearts seek their maiden league title since the 1960s.
Rodgers has seen it all before at Celtic - both perfect and shaky beginnings to a season. He's yet to finish second best.
But on the weekend's performance, this Edinburgh outfit showed they deserve serious consideration.
Hearts started with the confidence of a side unbeaten in the league this season - fans' favourite Kyziridis poked a cross in for Shankland to stab wide.
The Glasgow team didn't help themselves with some unusual sloppiness in possession and they faltered under their initial test.
A headed effort from Braga was touched on to a post by Kasper Schmeichel and the follow-up from Shankland was turned into the net by the hapless defender, in for the absent center-back.
Celtic grew into the contest and started building moves. From a flowing attack, Sebastian Tounekti released the full-back to set up McGregor, who rolled in.
Aside from the Nygren chance, Celtic struggled to create much for striker Kenny or his replacement Shin Yamada amid the absence of stricken attackers their key strikers.
Hearts rediscovered their energy and versatility in creating chances in the opposition half. The Greek forward, one of the finds of the club's relationship with shareholder Tony Bloom's Jamestown Analytics, struck low past the goalkeeper from the just outside the area.
Immediately after, the defender fouled Braga in the right side of the box and the penalty taker converted. And it could've been an more comprehensive victory, had substitute Ageu not been denied by Schmeichel.
The visitors' performance after the break was partially encapsulated in a couple of moments involving big-money recruit Engles.
The set-piece from Engles delivery was in sharp opposition to his European display in the Europa League win over their Austrian opponents and the Belgium international was then booked for a professional foul.
The Hearts manager: "You see how hard the players work, the team spirit. That's not always enough to win games consistently.
"What we have got, is good technical ability. You're witnessing it from a lot of players who have been here before. Recent additions are keen to demonstrate their quality.
"We've got a good thing going at the minute, but it's only three points. It's important for us to keep winning. We've got loads to do, plenty to improve. Following the initial fixtures is typically a benchmark of your standing."
The Celtic boss: "It's a really poor goal from our perspective. We failed to push up when the ball went back as a line so when they pass the ball, they ought to be caught offside but weren't. We have got to improve with the shot.
"There's still so many points to play for. It's only the beginning. It's just nine matches. Obviously, being eight adrift is not ideal. The comfort is there's so many games to play.
"Our attention must turn on the here and now and look to achieve greater stability and more quality in our play."
The Glasgow club are returning to their stadium on Wednesday against promoted side Falkirk (evening kick-off). At the identical hour in the Scottish Premiership, the Edinburgh outfit are at their opponents' ground.
Mira Thorne is a seasoned slot gaming analyst with over a decade of experience, specializing in strategy development and game reviews.