DALLAS (AP) — Joe Mazzulla is a big fan of UFC matches and splices highlights of fights into some of the basketball video he shows the Boston Celtics.

He doesn’t do it for entertainment purposes or to make players laugh. He does it for a 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, the second-year Celtics coach. “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, they were.

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 this series. Boston frittered away almost all of what was a 21-point lead before winning 106-99 to take a 3-0 lead in the NBA Finals, moving one win away from what would be their record-setting 18th championship.

“Our guys have a great basketball IQ and have a great understanding of are we 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, they have an innate ability to control the runs of the game with the philosophy that we have.”

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 that play, and the Mavs were without their best puncher in what amounted to the 12th round of this fight.

“We couldn’t play physical,” Doncic said. “I don’t know. I don’t want to say nothing. … C’mon, man.”

Doncic fouled out with the Mavericks having gotten within three; 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; that lead 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 basically 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.

“Closer you think you’re going to submit someone, 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.”

BOSTON (106)

Brown 12-22 4-5 30, Tatum 11-26 5-5 31, Horford 3-6 0-0 8, Holiday 4-9 0-0 9, White 4-10 4-4 16, Hauser 3-4 0-0 9, Tillman 1-1 0-0 3, Pritchard 0-4 0-0 0. Totals 38-82 13-14 106.

DALLAS (99)

Jones Jr. 1-2 0-0 2, Washington 3-9 4-6 13, Gafford 3-3 0-0 6, Doncic 11-27 4-4 27, Irving 13-28 5-5 35, Kleber 0-2 0-0 0, Hardaway Jr. 0-5 0-0 0, Lively II 5-6 1-1 11, Exum 1-1 0-0 2, Green 1-2 0-0 3, Hardy 0-1 0-0 0. Totals 38-86 14-16 99.

Boston	30	20	35	21	—	106
Dallas	31	20	19	29	—	99

3-Point Goals–Boston 17-46 (White 4-9, Tatum 4-13, Hauser 3-4, Horford 2-5, Brown 2-9, Tillman 1-1, Holiday 1-3, Pritchard 0-2), Dallas 9-25 (Irving 4-6, Washington 3-6, Green 1-1, Doncic 1-7, Jones Jr. 0-1, Kleber 0-1, Hardaway Jr. 0-3). Fouled Out–Boston None, Dallas 1 (Doncic). Rebounds–Boston 36 (Brown 8), Dallas 43 (Lively II 13). Assists–Boston 26 (Brown 8), Dallas 15 (Doncic 6). Total Fouls–Boston 19, Dallas 17. A–20,311 (19,200)