Brilliant: Sixers coach Doc Rivers makes all the right moves to beat Boston without Joel Embiid

BOSTON — The Boston Celtics and their coaches share an entrance tunnel to the court at TD Garden with the common media. As rookie coach Joe Mazzulla led his staff back to the floor from halftime, he walked with a glazed, stunned look on his 34-year-old face.

With good reason. He was about to get his butt handed to him by a legend, and he seemed to know it.

Mazzulla’s star-studded team had dominated offensively, rolled through the Sixers’ defense in the absence of MVP favorite Joel Embiid, using backdoor cuts and the secondary break, but it led by only three points at halftime.

Mazzulla could hardly have asked for more. But he only led by three. And Doc Rivers had something for him.

» READ MORE: Overcoming Joel Embiid’s absence, Sixers take Game 1, 119-115, behind James Harden’s 45 points

He had lost the league’s two-time scoring leader but changed the offensive scheme in a week. A second-half adjustment. Steadfast faith. And last-minute level-headedness you only see in Hall of Fame coaches helped Rivers’ team secure a 119-115 upset thriller. Mazzulla is a fine young coach. There will be better nights for him.

Monday was Doc’s night.

“Doc coached great,” said team president Daryl Morey in the hallway afterward. Morey, for a change, understated matters.

These moments are precious in the Book of Doc. He was coach of the year as a rookie with the Orlando Magic in 2000. He won a title in Boston in 2008. But since then he’s battled injury and chemistry and LeBron James and Steph Curry, and he’s blown three 3-1 postseason series leads, more than any coach in NBA history. He oversaw the top-seeded Sixers’ 2021 second-round collapse against the fifth-seeded Hawks. He’s 5-0 in this year’s playoffs, and he’s 2-0 without Embiid, but ...

One title. Many collapses. But so many nights like Monday, when he was back at his best in Boston.

Rivers devised an attack that featured guard James Harden. Harden tied his playoff career high with 45 points, went 17-for-30, and hit 7-of-14 three-pointers, including the winner.

Doc flashed a matchup, 2-3 zone defense in the second half. The Celtics got just two more backdoors.

“We’re long, and quick,” Rivers said. “It saved us in the second half.”

Doc stuck with Paul Reed, who was baffled by the Celtics’ offensive scheme and was often frozen on offense himself several times, running to the wrong place, not setting screens, or screens on the wrong side of the ballhandler, allowing offensive rebounds. Harden and P.J. Tucker fiercely reprimanded Reed both on the court and in the huddles, but Doc stayed steady. Reed delivered him 10 points, 13 rebounds, and sank four free throws on four chances in the final 57.1 seconds.

“I was really happy for Paul,” Rivers said. “A couple of guys really got into him. It was close to excessive. I kept him in. I said, ‘Go win the game. Go do something for us.’”

» READ MORE: James Harden emerges from the grave to give Sixers wild Game 1 win. Now, all they need is Joel Embiid.

Then, with 26 seconds to play, with the score tied, and with Jayson Tatum on the free throw line with one more foul shot, Rivers delivered his coup de grâce.

He sent soft rebounder Georges Niang, a three-point specialist, into the game for Reed. The thinking: Spread the floor for the Sixers’ final possession, hoping Harden would attract a favorable matchup against one of the Celtics’ big men. The hope: Tatum would make the second free throw, so the Sixers wouldn’t have to rebound at a disadvantage.

“We put Georges on the floor, took Paul out, went all smalls, which was scary,” Rivers admitted. “They miss a free throw. .... We just took that gamble. I don’t know if that would have gone well there.”

Tatum made it, for a one-point lead, but Rivers didn’t call a timeout. That would have been panic. That would have given the Celtics a chance to regroup defensively. The Celtics didn’t have a timeout to call.

“I did not want to use that timeout,” Rivers said. “I just didn’t want them to be able to set their defense up.”

Did Doc worry that Harden would be double-teamed?

“I think they would have,” Rivers said.

It worked. Perfectly.

Niang set a screen. His defender, center Al Horford, switched onto Harden. Harden dropped a 26-foot three-pointer in Horford’s face with 8.4 seconds to play to make it 117-115.

“It was great coaching, not letting them set up their D,” Harden said. “I got my shot.”

And he made it.

That hasn’t happened enough in Doc’s 23-year coaching career, but it’s happened a lot. He’s ninth, with 1,096 regular-season wins, and second among active coaches, so he’ll finish his career even higher. His 109 playoff wins rank fourth, and he’s second among actives there, too.

And, oh, that 109th ...

Chef’s kiss.