After letting his starters run roughshod over Philadelphia’s backups the previous night, Celtics coach Joe Mazzulla handed the reins to his reserves on Sunday.

Mazzulla gave Jayson Tatum, Jaylen Brown, Jrue Holiday, Derrick White, Luke Kornet, Xavier Tillman and Al Horford the night off as Boston welcomed the Raptors to TD Garden for the penultimate game of its preseason schedule.

Toronto played its regulars, but they were no match for the Celtics’ subs, who led by 21 points after one quarter and 34 at halftime before holding on for a 115-111 victory. Boston improved to 4-0 this preseason with one exhibition remaining.

This game was a chance for depth players to make their cases for rotation minutes and roster spots. Jordan Walsh and Lonnie Walker IV both capitalized.

Momentum has been building for Walsh since Boston’s preseason opener in Abu Dhabi, and the 2023 second-round pick delivered another encouraging performance, turning in a 16-point, 10-rebound double-double. Walsh shot 50% from the floor (6 of 12) and was active on the offensive glass.

Walsh, who’s still the youngest player on the Celtics’ roster, is making a compelling argument for playing time after spending nearly his entire rookie season in the G League.

“Just having an understanding of what his job is: defend at a high level, defend multiple positions, rebound and then make reads on the offensive end. So he’s doing a great job,” Mazzulla said. “I’m just really proud of his growth. … It’s been fun to watch him grow.”

Financial considerations could prevent Walker — a seventh-year veteran in camp signed to an Exhibit 10 tryout contract — from landing Boston’s final open roster spot, which likely would mean a trip to Maine to open the season. But the 25-year-old wing now has made a positive impression in back-to-back games.

Against Toronto, Walker shot it well from outside (4-for-9 from three) and showed good touch while attacking the rim, converting a series of contested layups from tricky angles. A 9-foot floater that put the Celtics up 31 prompted a “too small” celebration from the former Brooklyn Net.

On one first-quarter possession, Walker drove toward the basket and dished a pass to center Neemias Queta. The 7-footer couldn’t finish at the rim, but Walsh snatched the offensive rebound, spun and found Walker, who buried a second-chance three.

Walker has said since his arrival in Boston that he wants to prove he can be more than just a scorer, and he didn’t exactly accomplish that Sunday, with one assist and zeroes in the rebounds, steals and blocks columns. But he played the role of bucket-getter well, finishing with 20 points on 8-of-15 shooting.

Queta missed his first six field goals but had 11 rebounds and five assists in the first half and was 6-for-6 from the free-throw line, finishing with 12, 15 and five.

One Celtics hopeful who scuffled was guard Jaden Springer. The young guard picked up two quick fouls and committed one turnover, after which Mazzulla immediately reinserted Walker. Springer didn’t see the floor again until the fourth quarter.

Springer, acquired from the 76ers in February, was part of Boston’s second unit for both games in Abu Dhabi, then did not play Saturday night against his former team. His $4 million salary this season is guaranteed.

On a positive note, Springer did hit both of his 3-point attempts.

It also was a quiet night for Boston’s rookies. Consistency still is eluding first-rounder Baylor Scheierman, who went 0-for-6 from the floor and missed five threes in his 14 minutes. Scheierman is just 3-for-17 from deep this preseason. Second-rounder Anton Watson played the full fourth quarter and was a team-worst minus-18.

Payton Pritchard continued his strong preseason with 19 points on 7-of-13 shooting (5-for-11 from three). The other core rotation player who suited up for Boston, Sam Hauser, couldn’t keep up his torrid pace from the previous two games, going 2-for-11 and 1-for-7 from deep.

Two-way player Drew Peterson handled much of the second-half scoring load for the Celtics, pouring in 23 points while shooting efficiently from the floor (6 of 9), 3-point line (3 of 5) and foul line (8 of 10).

Horford to debut Tuesday

After sitting out the Celtics’ first four preseason games, Horford will log minutes in Tuesday night’s exhibition finale in Toronto, per Mazzulla.

“He’ll play on Tuesday. He’s good,” Mazzulla said of the 38-year-old, who’s entering his 18th NBA season. “He’s ready to go. He’s ramping up, getting in shape, working hard. He’ll play on Tuesday in Toronto.”

Horford, Kornet, Tillman and Queta all will factor into Boston’s plan to replace rehabbing center Kristaps Porzingis, but it’s unclear how Mazzulla intends to divvy up minutes between his four frontcourt fill-ins.

At his age, Horford isn’t likely to see a traditional starter’s workload in Porzingis’ absence, and Mazzulla left open the possibility of starting Kornet and bringing Horford off the bench.

Porzingis said before training camp that he hopes to return by the end of December, if not earlier. The team was “very, very pleased” with the progress he made during the offseason, according to Brad Stevens.

Still a rookie (for now)

Walsh’s rookie season ended in an NBA championship, but the 20-year-old hasn’t been able to shed his rookie status. Not yet, at least.

He revealed after Sunday’s win that he’s still considered a rookie in the eyes of his Celtics teammates until his second season tips off.

“Until we get our rings, I’m a rookie,” Walsh lamented with a smile. “It is tough. I don’t agree with that.”

His most memorable bit of first-year hazing was delivered not by a veteran teammate, but by Mazzulla. According to Walsh, the head coach made him dance to a Boyz II Men song during a team meeting last season.

“They played a song by Boyz II Men in the film room, and I had to get up and dance in front of everybody and sing the song, and I had never heard the song ever in my life,” Walsh said. “So it was Joe’s (way of) embarrassing me in front of everybody. … So I got up there and danced, and it was pretty embarrassing, for sure.”

Off the rim

White, Horford and Kornet watched from the bench in street clothes, with Konet sitting on the floor along the baseline. The rest of Boston’s resting starters weren’t spotted during the game. … Tillman’s DNP was notable, as it suggested Mazzulla views him as a key piece. The 6-foot-8 big man has shown marked improvement as a 3-point shooter this preseason, making 80% of his attempts (6-for-8).