New Orleans’s Zion Williamson gets ball knocked out of his hands from behind while Celtics center Daniel Theis defends Sunday in New Orleans. Williamson scored 28 points to help the Pelicans rally for a 120-115 overtime win. Gerald Herbert/Associated Press

NEW ORLEANS — Brandon Ingram and Zion Williamson took what they hope will be meaningful steps in turning the New Orleans Pelicans’ season around, combining decisively to produce pivotal plays during a memorable comeback.

Ingram highlighted a 33-point performance by hitting a go-ahead 3-pointer with 33.3 seconds left in overtime, and New Orleans held on for 120-115 victory over the Boston Celtics on Sunday after rallying from 24 points down in the third quarter.

“Today was a day of encouragement,” Ingram said. “We just stayed together and everybody did things that they do well.”

Zion Williamson scored 24 of his 28 points after halftime and had 10 rebounds, four assists and a block for the Pelicans, who narrowly avoided losing for the sixth time in seven games. Josh Hart, who was instrumental in the comeback, had 17 points, 10 rebounds, three blocks and a steal.

“We stayed true to who we were. We rallied back,” Williamson said. “Everybody – coaches, players, ball boys – everybody was just engaged.”

Jayson Tatum had 32 points and nine rebounds, and Jaylen Brown scored 25 for the Celtics, who appeared to be cruising to their third victory in four games when Tristan Thompson’s free throws gave Boston a 79-55 lead in the middle of the third quarter.

“We kind of got away from what got us the lead, not moving the ball, guarding, and they stormed back,” Brown said. “This one definitely hurts. It’s tough. Just a tough loss – a game we 100 percent should have won.”

Added Tatum, “If we want to be a really good team, we’ve got to put teams away early, especially being up 20-some points.”

The Pelicans finished the third quarter on a 19-8 run, capped by Williamson’s layup after he drove nearly the length of the court to score with less than 2 seconds on the clock.

The momentum carried into the fourth.

Williamson’s putback dunk ignited a 10-2 run during which Hart scored eight points. Hart made a driving layup as he was fouled, a 3-pointe and a reverse put-back after Lonzo Ball’s fast-break layup was blocked by Daniel Theis.

New Orleans pulled even when Ingram’s transition 3 made it 98-all with 4:10 left.

The lead changed hands twice in the last 11 seconds of regulation, with Tatum draining a fallaway to make it 106-105 and Williamson hitting a layup as he was fouled for a three-point play that put the Pelicans up 108-106 with 6.9 seconds to go. Tatum then sank a driving floater in the final second to force overtime.

The game was tied at 112 when Ingram’s 3, set up by Williamson’s pass, put the Pelicans in front to stay.

The Celtics controlled most of the first half, scoring 19 points off 10 New Orleans turnovers.

Tatum exploded for 17 points in the second quarter, when Boston led by as many as 19 before taking a 63-47 lead into halftime.

“We played exceptionally well for a large part of the time,” Brown said. “We just got to mature and grow up.”

TIP-INS

Celtics: Coach Brad Stevens said Marcus Smart, who has not played since injuring his calf during a Jan. 30 loss to the Lakers, is traveling with the team. But while Stevens said Smart has been “going at a decent rate the last few days,” he stressed that it remains uncertain when Smart will be ready to return to the lineup. … Boston fell to 14-5 when leading at halftime. … Thompson and Kemba Walker each scored 14 points and Aaron Nesmith scored 10. … Robert Williams III grabbed 13 rebounds, blocked four shots and scored eight points. … Boston shot 39.8% (39 of 98), including 10 of 27 from 3-point range.

Pelicans: Ball scored 16 points and Willy Hernangomez had 13 rebounds. … JJ Redick was ejected after a pair of technical fouls in the first minute of the fourth quarter. His first technical came while arguing, the second after he hastily bounce-passed the ball to an official after Boston’s Nesmith was called for fouling him on a drive. … New Orleans missed six straight free throws in the third quarter and finished 25 of 37 for the game from the foul line. … The Pelicans shot 44.7% (42 of 94), including 11 of 36 from deep.

LEARNING EXPERIENCE

Van Gundy was gratified the see his club rally from a big second-half hole just one game after seeing an 11-point fourth-quarter lead turn into an 18-point loss during a dreadful final 12 minutes against Phoenix on Friday.

“The last two games – right there – are about all the lessons that our team needs,” Van Gundy said. “You’ve just got to play through everything and keep fighting, play possession by possession by possession from night to night and from minute to minute. … Things change very, very quickly in this league, in games and in seasons. Just keep fighting.”