Tyrese Haliburton and the Indiana Pacers savoured "a very special" night after they saw off the Boston Celtics in the closing stages of a dramatic in-season tournament quarterfinal.

Indiana has reached the final four stage in Las Vegas and will face the winner of Tuesday's game between the New York Knicks and Milwaukee Bucks in the semifinals.

The Pacers won 122-112 on Monday, spurred on by a tiebreaking four-point play from Haliburton with 1:33 left, which delighted an electric home crowd and sparked a decisive 9-0 run.

Haliburton had 26 points, 13 assists and 10 rebounds to record his first career triple-double at the perfect time, putting his team two wins away from NBA Cup glory.

He had missed Saturday's win over the Miami Heat with a respiratory infection and conceded he felt "dead" in a first half where he struggled with his breathing, but after using an inhaler at halftime the 23-year-old was able to produce a memorable second-half performance that led his team to a famous victory.

Haliburton was thrilled to upset the odds against Boston, who blew out Indiana 155-104 in November and came into the quarterfinal with a league-leading 15-4 record.

"We have wanted to be in this situation all year – and here we are," Haliburton said, per ESPN.

"Now it's not just about being here. It's about winning.

"It feels good to win, especially in a game where nobody expected us to. The atmosphere was crazy.

"It means the world to me to represent Indiana and this organization. I don't even know if it was as much about what was at stake, as it was about what they did to us the last time. I think that left a bad taste in our mouths."

Pacers coach Rick Carlisle felt the tournament clash was like a playoff game.

"The thing about the in-season tournament is that as you advance, you're going to play two more games – win or lose in the quarterfinals – against better opponents," he said. 

"And so this is something that's great for us because we need high level competition. 

"It really is another thing that is a simulator of playoff basketball. So it really helps us. And so, coming out with the win was big for a lot of reasons that I mentioned.

"But I know this is very special to Tyrese as well."

Center Myles Turner has been with the Pacers since 2015 so is well qualified to put the atmosphere and occasion into context.

"I haven't heard it like this here in like three or four years, probably since Victor Oladipo was here," he said after scoring 17 points and adding 10 boards.

"The energy was just incredible. I think this city really started rallying around this team. The story, the backstory of it all makes it the most special.

"And the fact that he [Haliburton] got his opportunity, he is able to take it and run with it ... I mean, it's just dope to see where this franchise, where I started with to what it's becoming and what it potentially can become from the same level. 

"It's honestly, like I said, it goes back to the atmosphere. I haven't heard MVP chants, maybe when Oladipo was here, but Ty's really come in and taken over and it's fun stuff."

Jayson Tatum had 32 points and 12 rebounds for Boston, while Jaylen Brown scored 30 points and added nine boards.

But those efforts were still not enough to prevent elimination as Boston played without injured All-Star Kristaps Porzingis.

The defeat left Tatum disappointed to miss out on the Las Vegas showpiece as the in-season tournament continues to gain momentum and popularity.

"We got to just be more connected defensively," he said. "But, I mean, it's the NBA. Sometimes guys are going to make plays.

"He [Haliburton] hit some tough shots. So it's kind of two fold. Guys get paid a lot of money to play basketball, and they're pretty good.

"Yeah. I wanted to go to Vegas, I didn't want to go home. I wanted to go Vegas, so yeah, I'm mad. Next year, I guess."

Indiana's semifinal will be on Thursday, a day before Boston hosts the loser of the New York-Milwaukee quarterfinal in their next game.