Though he made his Celtics debut more than a week earlier, Saturday night was Lonnie Walker IV’s first real opportunity to prove himself to Boston’s decision-makers.

The veteran wing played a team-high 25 minutes in the Celtics 139-89 throttling of the Philadelphia 76ers at TD Garden, more than doubling his total from the first two preseason games combined (11).

Walker scored 11 points on 4-for-7 shooting (1-for-4 from 3-point range). He also dished out seven assists, snatched four rebounds, blocked one shot and added two steals while playing against a rotating cast of Sixers benchwarmers.

The competition was far from stiff — Philly sat all of its starters and most of its veteran reserves in the blowout loss — but Celtics coach Joe Mazzulla liked what he saw from Walker, who signed an Exhibit 10 tryout contract with Boston after failing to land a guaranteed deal in free agency.

“I think he’s been really good,” Mazzulla said. “I think it’s an adjustment coming here because it’s just a different style of basketball, and I like his open-mindedness to learning. I like his patience. It’s funny when you get a guy like him who’s been in the league for seven years.

“I saw some things from him today that he might not think are important, or other people won’t, but they’re really, really important things, defensively and then offensively. Whether it was his positioning or whether it was a small cut that he made or a read that he made, those things go a long way because they open up opportunities.”

For Walker, who didn’t see the floor until the fourth quarter in the Celtics’ two exhibition games in Abu Dhabi, this was his first chance to test his chemistry with some of Boston’s regulars. He was part of Boston’s second unit with the likes of Payton Pritchard and Sam Hauser, then later repped alongside players lower down the depth chart.

“This is really my first time getting my feet wet as far as playing with the team — as far as even getting reps in general,” Walker said. “… This is my first time playing with Payton and all the other guys and stuff. So really just figuring out on the fly trying to find where my comfort zone is.

“But overall, I give myself — it was OK. I think there’s room for improvement, and the only way I can get better is continuously watching film and see what I can get better at.”

Based on his experience (322 career appearances, 88 starts, meaningful playoff minutes as recently as 2023), Walker should be overqualified for his E-10 deal, which features no guaranteed money and could ultimately result in a trip to the G League. But the 25-year-old reported to training camp humble and hungry, saying he’ll accept whatever role he earns.

“Being one of the first people in the gym and one of the last people out, coming in at night to get shots up,” said Walker, who’s been one of the final players to leave the court after each Celtics practice. “I’m doing everything in my power to make sure I’m mentally and physically prepared for whatever might be happening.

“If things do go how it’s supposed to do, then I’ll be happy. If it don’t go how it’s supposed to be, then at the end of the day, I can tip my hat off as a man, to understand that I did everything in my power to do what I could.”

Walker has two games left to show Mazzulla and president of basketball operations Brad Stevens that he deserves the final open spot on Boston’s 15-man roster. The Celtics close out their preseason with a home-and-home against the Raptors — at TD Garden on Sunday night, then in Toronto on Tuesday.

“He’s enjoying just working hard,” Mazzulla said.