DALLAS -- Luka Doncic stared at the official in angry disbelief after he was whistled for his sixth foul and then turned his head toward the Dallas Mavericks bench to demand that the called be challenged.

After a replay review, the challenge was deemed unsuccessful, banishing Doncic to the bench for the final 4 minutes, 12 seconds of Game 3 of the NBA Finals.

Dallas, down 21 early in the fourth quarter, had pulled within three points when Doncic was disqualified. He helplessly watched as the Mavs' rally fell short in Wednesday's 106-99 loss to the Boston Celtics at American Airlines Center, putting Dallas on the brink of being swept.

Doncic, who fouled out for the first time in 48 career playoff games, was called for four fouls in the fourth quarter.

"We couldn't play physical," Doncic said when asked about the officiating. "I don't know. I don't want to say nothing.

"You know, six fouls in the NBA Finals, basically I'm like this," Doncic said, motioning with his palms up. "Come on, man. Be better than that."

The referees weren't the only reason for Doncic's frustration.

He got off to a sizzling start, making five of his first seven shots from the floor as the Mavs jumped out to a 13-point lead in the first quarter, but he struggled offensively for most of the remainder of the game. Doncic finished with 27 points on 11-of-27 shooting.

The Celtics also relentlessly hunted Doncic on defense, as the Mavs star is dealing with a thoracic contusion suffered during Game 1 and has been playing on a sprained right knee most of the season. According to ESPN Stats & Information data, Boston scored 16 points on 6-of-15 shooting with Doncic as the primary defender. The Celtics also generated several good looks by penetrating against Doncic to force the Dallas defense to rotate.

"He's definitely got a bull's-eye on his chest," Mavs coach Jason Kidd said. "He's got to be able to guard and understand that we're there to protect him and help him if he does get beat. Again, he's carrying a load offensively. They are putting him in every pick-and-roll and iso. He's got to be able to play the game where he can rest on offense and let others carry the load."

Mavs guard Kyrie Irving, who struggled during the two losses in Boston to open the series, broke out of his mini-slump with 35 points on 13-of-28 shooting.

The rest of the Mavs combined to score only 37 points, as Kidd stretched his rotation to 11 players in a desperate search for contributors.

Dallas was on a 20-2 run when Doncic was called for his sixth foul after attempting to take a charge against Boston star Jaylen Brown on the left wing. It occurred only 26 seconds after Doncic's fifth foul, which was called when he got tangled up with Brown while defending a post-up.

Doncic animatedly expressed his angst to the officials after both of those calls, as he did on several other occasions throughout the game.

"You just got to let it breathe a little bit," Irving said when asked what his postgame message to his co-star would be. "Let the human emotions come out. Just give him a hug. That's it, man. It's easy to point the finger at just him, say, 'You could be better.' That's easy to say. I think he knows that. But, yeah, it's reiterating that I have his back, we all have his back."

Dallas now faces daunting odds. Teams are 0-156 in playoff series after falling behind by a 3-0 deficit in NBA history.

"It's not over until it's over," Doncic said. "We just got to believe."