Kelly Olynyk still can’t believe the Bruins lost Game 7 to St. Louis in the Stanley Cup final.

He has, however, far less difficulty understanding how his old team and current club have crashed the party at the top of the Eastern Conference as we sidle up to the quarter pole of the 2019-20 season.

But while the Celtics were a mystery team of sorts after losing three starters, there was still the expectation they would have a puncher’s chance against Milwaukee, Toronto and Philadelphia. Olynyk’s Heat, on the other hand, have raised more than a few eyebrows as they carried a 15-5 record into the Garden Wednesday night — a half-game ahead of the 14-5 C’s. Miami led here by as many as 11 in the second quarter, but with the Heat having gone overtime the night before to win in Toronto, the Celts eventually wore them down and pulled away, 112-93.

Pin this one on the schedule or simply the fact the Celtics are more than pretty good, but the Heat rise is still well worthy of note. Miami was a sub-.500 team at 39-43 last year. Then it said goodbye to its top two scorers, Josh Richardson and Dwyane Wade, and its No. 5 scorer and leading rebounder, Hassan Whiteside.

Into the breach stepped Jimmy Butler. But it’s been the undrafted Kendrick Nunn, the NBA’s Rookie of the Month for October/November, who’s caught most people off-guard. And fellow rook Tyler Herro has been a major factor, as well.

A bit unexpected to most, but not Olynyk.

“I don’t think so,” said the four-year Celt, who needed 15 tickets last night to take care of friends he’s maintained in the area. “I mean, every team believes that they’re going to be good. It’s expect the unexpected, I guess.

“But, for us, we’ve got a great group of guys that play well together, want to play together, play for each other — kind of a lot like our group in Boston before I left. We just gelled on both ends of the floor. People are enjoying each other’s successes. It’s a real team. It’s a team atmosphere, a team environment, and, you know, we’re playing like it. And when you don’t play like it and guys are kind of doing their own thing and splintering from the core, it shows. So I think for us, it’s all about being together on both ends of the floor and just enjoying an NBA season together.”

Sounds a bit like the current Celtics and unlike the edition that preceded it.

“To start off, we’ve taken care of what we’ve needed to take care of,” Olynyk said. “Against non-playing teams, we’ve won those games. We were a team last year who could play up with anybody but also play down to anybody, record-wise. I think this year we’ve been way more consistent in our play, and I think that’s shown.”

And then there’s the Butler factor.

“He’s just brought a super-competitive edge,” said Olynyk, who had 12 points Wednesday. “(He’s) obviously a guy that we can throw the ball to and he can make something happen.

“But I think that what Jimmy’s brought to us is a super-unselfish environment on and off the court. He’s just a really unselfish player who can do a lot of things obviously. He’s super-multidimensional as a basketball player, and it’s shown through the first, whatever it is, 20 games what he can do for us. It’s just given us a whole other dimension, being able to throw him the ball in different situations and have him create, whether it’s for himself or for others.”

As Brad Stevens put it before tipoff, “You add Butler to that team, I mean, I think they’re really good.”

He added of Nunn, “He’s excellent. He’s having a great year. And Duncan Robinson and Herro have added just ridiculous shooting. So that has opened up the floor for those other guys. So I would say Butler’s addition, you knew they were going to be in the mix at some level, but I think they’ve all been elevated by all those guys.”

The Celtic elevation has been no less interesting. The C’s lost three starters from last year’s crew and have played far better.

“And they’ve had guys in and out of the lineup, too, and they’ve all turned out production in a great way,” Olynyk said, referring to the absences of Gordon Hayward and Marcus Smart on Wednesday. “They’ve had guys step up, and that’s something Brad’s always been good at — injecting guys into lineups and different rotations. Guys have stepped up to the plate, and they’re playing good basketball, especially here at home.”

Olynyk still keeps up with his former team, even though Smart and Jaylen Brown are the only ones remaining from his last season here, 2016-17. And as a true Canadian, he follows the NHL, which had him shaking his head last June when the Blues skated around TD Garden with the Cup.

But he’s big on the B’s this year.

“Yeah, man, they’re good,” Olynyk said. “They’re REALLY good.”

But that’s less of a shock than the early seasons of the Celts and Heat.