Boston Celtics forward Jayson Tatum beats Dallas Mavericks forward PJ Washington to the basket during Game 3 of the NBA Finals in Dallas, Texas, on Wednesday. The Celtics held off a furious Dallas rally to win 106-99 and take a 3-0 stranglehold on the series.

DALLAS — Joe Mazzulla is a big fan of UFC and splices highlights of the bouts into some of the basketball videos he shows to the Boston Celtics.

He doesn't do it for entertainment purposes or to make players laugh. He does it for one simple reason. He wants the Celtics to have a fighters' mentality.

"If you've ever been in a fight with someone, and you think you're about to beat 'em, you usually get sucker-punched," said Mazzulla, currently in his sophomore year at the helm of the Celtics. "The closer you are to beating them up, the closer you are to losing."

Translation: He wanted the Celtics ready for a fight, and, in Game 3 of the NBA Finals, that's just what they got.

A pair of big runs — 23-8 in the first half, 20-5 in the second half — represented what became the knockout blows in this game, and maybe the series. Boston frittered away almost all of what was a th21-point lead, before clinching the game at the death 106-99 and putting it one game away from what would be a record-setting 18th championship.

"Our guys have a great basketball IQ and have a great understanding of whether we are playing the right way, taking the right shots and giving up the right shot," Mazzulla said. "They know exactly when we are not doing that. So, with the philosophy that we have, they have an innate ability to control the runs of the game."

As is often the case with fights, the judges — in this case, the referees — had a big decision to make, and it wasn't one that was popular. Luka Doncic fouled out with 4:12 remaining, a call that held up under review, despite Dallas' arguments that Jaylen Brown initiated the contact on the play. It left the Mavs without their hardest puncher in what amounted to the 12th round of the fight.

"We couldn't play physically," Doncic said. "I don't know. I don't want to say anything."

Doncic fouled out with the Mavericks having played their way to within three. However, there was no miracle finish. Boston did enough to hang on, and now a championship could be in its hands as early as Friday night when the teams meet in Game 4.

And the big punch — sometimes early, sometimes not — has been a theme for Boston throughout this series. Dallas ran out to a 25-12 lead early Wednesday, a lead that was basically gone by the end of the first quarter.

"We expected their first punch," Celtics forward Jayson Tatum said.

Control of Game 1 was seized early with a 23-5 run by the Celtics. In Game 2, a 15-4 run in the second half proved to be the difference. In Game 3, there were the two big spurts.

Mazzulla warned the Celtics that any spell where focus is lost could cost them games. Clearly, they've listened.

"The closer you think you're getting to someone submitting is usually when you get submitted," Mazzulla said.

There's no championship belt, like the ones fighters get, coming when this series is over, but the trophy is within sight now.

"We've got to keep fighting," Tatum said. "We can't relax."

Kristaps Porzingis did not play on Wednesday night because of a tendon injury in his lower left leg that was incurred in the previous game.

"The medical team and the staff decided it wasn't what was best for him," Mazzulla said about Game 3. "It'll just be a day-to-day thing, see how he is tomorrow, and the next day. He didn't look right. That was it. I was not involved in it. It was out of his hands."

The 28-year-old Porzingis had missed 10 consecutive playoff games because of a right calf strain, before returning last week for the start of the Finals. He helped the Celtics take a 2-0 series lead against his former team, jump-starting the Celtics with 11 points and two blocks in the first quarter of the Game 1 win, then shot 12 points in Game 2.