The first Celtics-Raptors matchup of the season was an overtime thriller decided on a last-second 3-pointer.

Round 2 was the polar opposite.

Boston manhandled a rebuilding and shorthanded Toronto squad Tuesday at TD Garden, winning 125-71 to close out 2024 on a positive note.

The 56-point victory was the second-largest in franchise history, trailing only a 56-point waxing of Chicago on Dec. 8, 2018. It also was a palate-cleanser for Boston after an inconsistent December that included losses in four of their previous six games.

Joe Mazzulla’s club now will head out West for the first time this season, kicking off a four-game road trip Thursday night in Minnesota.

Jayson Tatum scored 18 of his 23 points during an overpowering third quarter for the Celtics, who outscored the Raptors 45-18 in the frame after holding a 10-point lead at halftime. Derrick White scored an efficient 16 points (6-for-8 shooting, 3-for-3 from 3-point range) and blocked four shots, and Jrue Holiday (14 points) went 4-for-5 from three and swiped three steals after missing three games with a shoulder injury.

Payton Pritchard delivered another standout performance off the bench, finishing with 19 points (5-for-8 from three), six rebounds, four assists and three steals. Mazzulla sat his starters after the third quarter and pulled top reserves Pritchard and Sam Hauser (12 points, 4-for-7 from three) shortly thereafter.

Jaylen Brown (12 points, nine rebounds, three assists, one steal) sported a large ice pack on his right shoulder late in the game after appearing to tweak it earlier. The Celtics played without starting center Kristaps Porzingis, who sat out his third straight game with a sprained ankle.

Though the Celtics made 50% of their 3-pointers in the win, their shooting was frigid to start the game: 0-for-8 from the floor, 0-for-6 from three and zero points in the first 4:25, with Brown finally breaking that drought with a driving layup.

But because the Raptors both are one of the NBA’s weakest teams and were playing without two of their top three leading scorers (RJ Barrett and Gradey Dick), they also made just one basket during that span. Once Boston found its groove, it surged ahead, scoring on five straight possessions, including four made threes.

White hit two of those triples as part of a 10-point first quarter that also featured one steal and two blocks, the second of which loudly denied Chris Boucher at the rim. White capped the quarter with a buzzer-beating floater that put Boston ahead 23-12. It was the fewest points the Celtics had allowed in a first quarter all season.

Pritchard also made two first-quarter 3-pointers and two more in the second, including a 32-foot long ball over Davion Mitchell. After missing their first 14 threes of the game, the Raptors converted five of their next seven, preventing the Celtics from adding to their lead during an erratic second quarter.

Boston seemingly prioritized interior defense against Toronto big man Jakob Poeltl, who put up 35 and 12 in the teams’ first meeting of the season. Poeltl attempted just one shot in the first half, though he was able to snag 10 rebounds against a Celtics team that was down its top frontcourt player in Porzingis.

The Celtics’ guards shot the ball effectively in the first half — White, Holiday and Pritchard were a combined 8-for-12 from deep — but the rest of their roster attempted 13 threes and missed all of them. Tatum scored just five first-half points for the second straight game. The Celtics, who came in averaging 119.5 points per game (fourth-most in the NBA), were nearly 20 points off that pace at halftime.

Yet Boston still led by double digits, 45-35, after an 80-point first half that was tied for the lowest-scoring in any NBA game this season. The Celtics then pulled away during a dominant third quarter, during which they doubled their scoring output and ballooned their lead from 10 points to 37.

Tatum snapped his cold spell by hitting back-to-back threes in the first two minutes after halftime. He scored 18 in the frame, as many as Toronto totaled as a team. The Celtics went 10-for-12 from three, poured in 45 points and then yanked their starters at the start of the fourth quarter, up 90-53.

Boston’s onslaught continued once the backups entered. The Celtics outscored the Raptors 35-18 in the fourth and got some quality minutes from Jordan Walsh, who went 4-for-6 from the floor and 1-for-2 from three in his second encouraging outing of the week.