At a glance
The dominant Edinburgh side powered eight ahead of their Glasgow rivals at the top of the Scottish Premiership to strengthen their early championship claims and worsen the struggles around Brendan Rodgers' side.
A superb goal from Kyziridis and Lawrence Shankland's penalty gave the Hearts team a 3-1 lead that the reigning champions could not overcome.
Dane Murray - one of three youngsters in the Celtic starting lineup - slashed into his own net early on to put Hearts ahead at a bouncing 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 Benjamin Nygren almost put Celtic in front, opting for finesse over power and allowing Alexander Schwolow to make a crucial stop.
But Derek McInnes' irrepressible Hearts seized control again to consign Celtic to back-to-back losses for the initial occasion since last year.
It also gives the Hearts a commanding advantage at the summit.
The last time they were this far ahead was in the 2005-2006 season under George Burley, when they ultimately finished second - one of just four occasions that a team has not secured the title having held such a lead in the last three decades.
The Hearts coach, whose former team were runners-up to the champions on multiple times, has been at pains to play down title talk, as Hearts seek their first top-flight crown since 1960.
Rodgers has experienced this previously at the club - both perfect and shaky beginnings to a season. He's yet to finish second best.
But on the weekend's performance, this Hearts team showed they need to be taken seriously.
The Edinburgh side started with the self-assurance of a side unbeaten in the league this season - the popular attacker poked a cross in for the striker to fire off target.
Celtic didn't help themselves with some uncharacteristic carelessness in possession and they buckled under their initial test.
Claudio Braga's header was tipped onto the woodwork by Kasper Schmeichel and the follow-up from Shankland was diverted goalwards by the hapless defender, in for the injured Cameron Carter-Vickers.
Celtic grew into the contest and started stringing passes together. From one such move, the midfielder released the full-back to square for McGregor, who rolled in.
Aside from the opportunity for Nygren, the visitors found it hard to generate chances for lone frontman Jonny Kenny or his substitute Yamada amid the absence of stricken attackers Kelechi Iheanacho and Daizen Maeda.
Hearts regained their intensity and adaptability in creating chances in the opposition half. Kyziridis, a standout performer of the club's scouting network, fired a low shot past Schmeichel from the edge of the box.
Immediately after, Murray tripped the midfielder in the inside right channel and Shankland converted. And it could've been an even more handsome win, had replacement Ageu not been stopped by Schmeichel.
The visitors' performance after the break was somewhat summed up in a couple of moments involving big-money recruit Engles.
The set-piece from Engles delivery was in stark contrast to his midweek exploits in the Europa League win over their Austrian opponents and the national team player was then yellow-carded for a cynical foul.
The Hearts manager: "You see how hard the players work, the team spirit. That's not sufficient on its own to win games week in, week out.
"What we have got, is skillful players. You're seeing that from a lot of players who have been here before. Recent additions are eager to show that.
"We've got a good thing going at the minute, but it's just one win. It's important for us to keep winning. We've got much work ahead, loads to do. Following the initial fixtures is normally an indication of where you are."
The Celtic boss: "The second goal was disappointing from our perspective. We failed to push up when the ball went back as a defensive unit so when they pass the ball, they ought to be caught offside but didn't. We have got to do better with the attempt.
"Plenty of matches to play for. It's still so early. It's only nine games in. Obviously, being eight points behind is not what we would want. The comfort is there's so many games to play.
"Our attention must turn on the present and look to achieve greater stability and more quality in our play."
The Glasgow club are returning to their stadium on midweek against promoted side Falkirk (evening kick-off). At the identical hour in the Scottish Premiership, Hearts are at their opponents' ground.