At a glance
Rampant Hearts powered eight ahead of Celtic at the top of the Scottish top flight to strengthen their early-season title credentials and worsen the struggles around Brendan Rodgers' side.
A superb goal from Kyziridis and Lawrence Shankland's penalty gave the Hearts team a two-goal advantage that the title holders could not overcome.
Dane Murray - one of three youngsters in the Celtic XI - slashed into his own net early on to put the home side ahead at a energetic Tynecastle, and it was the 22-year-old's foul that led to the spot-kick.
Callum McGregor's classy first goal of the season had quickly cancelled out the first goal, and Benjamin Nygren almost put Celtic in front, choosing placement over power and allowing the Hearts keeper 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 commanding advantage at the top of the table.
The previous occasion they were so far clear was in the 2005-2006 season under their former manager, when they ended as runners-up - one of just four occasions that a team has failed to win the title after building such an advantage in the past 27 years.
The Hearts coach, whose former team were second to Celtic on multiple times, has been working hard to play down title talk, as the club seek their maiden league title since the 1960s.
Rodgers has experienced this previously at Celtic - both flawless and stuttering starts to a season. He's never ended as runner-up.
But on Sunday's evidence, this Edinburgh outfit showed they deserve serious consideration.
Hearts started with the confidence of a side unbeaten in the league this season - the popular attacker poked a cross in for Shankland to stab wide.
The Glasgow team didn't aid their cause with some uncharacteristic carelessness in possession and they buckled under their initial test.
A headed effort from Braga was tipped onto the woodwork by Kasper Schmeichel and the follow-up from Shankland was diverted goalwards 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.
Apart from the opportunity for Nygren, the visitors found it hard to generate chances for striker Kenny or his replacement Shin Yamada amid the absence of injured forwards Kelechi Iheanacho and Daizen Maeda.
Hearts rediscovered their energy and versatility in attacking from across the final third. Kyziridis, a standout performer of the club's scouting network, fired a low shot past Schmeichel from the just outside the area.
Almost straight away, the defender tripped the midfielder in the right side of the box and Shankland converted. And it could've been an even more handsome win, had substitute Ageu not been stopped by Schmeichel.
Celtic's second half was partially encapsulated in a couple of moments involving big-money recruit Engles.
The midfielder's wayward free-kick delivery was in sharp opposition to his midweek exploits in the Europa League win over Sturm Graz and the Belgium international was then yellow-carded for a cynical foul.
Hearts head coach Derek McInnes: "The effort from the squad is evident, the togetherness. That's not always enough to win games week in, week out.
"Our strength lies in, is skillful players. You're witnessing it from a lot of players who have been here previously. Some of the new signings are eager to show that.
"We're in a positive moment at the minute, but it's just one win. It's important for us to maintain this form. We've got loads to do, plenty to improve. After the first two rounds is normally an indication of your standing."
Celtic manager Brendan Rodgers: "The second goal was disappointing from our perspective. We didn't move when the ball went back as a defensive unit so when they play it, they ought to be caught offside but weren't. We have got to do better with the attempt.
"There's still so many points to play for. It's only the beginning. It's only nine games in. Clearly, being eight points behind is not ideal. The comfort is there's numerous fixtures to play.
"We now have to focus on the here and now and look to achieve greater stability and better performance in our play."
Celtic are returning to their stadium on midweek against promoted side Falkirk (evening kick-off). At the same time in the top division, the Edinburgh outfit are at their opponents' ground.
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