The Boston Celtics were upset by the Indiana Pacers in the first game of the NBA In-Season Tournament's knockout round.

The Celtics head home despite getting a strong performance from their two best players.

Jayson Tatum had 32 points and 12 rebounds, and Jaylen Brown finished with 30 points and nine rebounds for the Celtics. But it wasn't enough to extend a three-game winning streak, with All-Star Kristaps Porzingis missing his fourth straight game because of a strained left calf.

After the game, Celtics coach Joe Mazzulla summed up the issue, according to NBC Sports Boston:

Said Mazzulla, “Turnovers. It's hard to withstand 18 turnovers. So when you turn the ball over, you just let them get out in transition. And I thought that we just lost our offensive purpose, just didn't take care of the ball. I think we have seven turnovers in the third quarter. So, do that against (the Pacers) and they make you pay.”

Despite the turnover issues, the Celtics fought back from an 11-point third-quarter deficit and managed to force seven fourth-quarter ties. But then Tyrese Haliburton's 27-footer drew a foul on Brown and ignited a Pacers 9-0 run that buried Boston.

The Pacers may have had some extra motivation beyond the NBA In-Season Tournament – in the two teams' first matchup on Nov. 1, Boston blew out Indiana 155-104 — posting the second-highest points total in franchise history.

The Pacers move on to play in Thursday's tournament semifinals at Las Vegas against the New York-Milwaukee winner Tuesday.

The Celtics host the loser of the New York Knicks-Milwaukee Bucks quarterfinal Friday.