One Celtics player was on the floor for the final 17-plus minutes of last Friday’s win over the Miami Heat and Saturday’s victory over the Toronto Raptors.

It wasn’t Jaylen Brown, who sat out the second game of Boston’s back-to-back with an illness. It wasn’t Derrick White (excellent against Miami), Payton Pritchard (superb in Toronto) or any Celtics veteran.

It was the youngest player on Boston’s roster: rookie Hugo Gonzalez.

Head coach Joe Mazzulla subbed Gonzalez in midway through the third quarter of both games and never lifted him, watching as the 19-year-old energizer helped turn a pair of tight contests into double-digit Celtics wins through steals, contested rebounds, cuts to the rim and all-around maniacal hustle.

Gonzalez logged a career-high 29 minutes against Miami, and Boston outscored the Heat by 22 points with him on the floor. Against Toronto, he played 28 minutes and was an eye-popping plus-37. His two-handed driving dunk with 3:14 remaining essentially sealed the win for the Celtics, which pushed them past the Raptors and back into third place in the Eastern Conference.

The slam also whipped the Celtics’ bench into a frenzy and capped Gonzalez’s first NBA double-double. He finished with 10 points, 10 rebounds, two steals, one block and no turnovers after notching 10 and 8 with two steals and a block against Miami.

For Mazzulla, who’s notoriously tough on young players, to trust his youngest with such heavy workloads in important conference matchups spoke volumes. Just two months into his NBA career, Gonzalez already looks like a draft steal for the Celtics at No. 28 overall. He entered Monday with the best total plus/minus of any NBA rookie this season (plus-111), ahead of third overall pick VJ Edgecombe (plus-94) and No. 2 selection Dylan Harper (plus-80).

What’s allowed Gonzalez to be so impactful, so early? Along with his high motor and physical tools, Mazzulla and teammates point to the years the 6-foot-6 wing spent with Real Madrid, one of Europe’s top clubs, before joining the Celtics. Though he was a deep reserve on Real Madrid’s senior team, the teenager was able to learn behind a group of veterans that included ex-NBAers Mario Hezonja, Serge Ibaka, Guerschon Yabusele and Rudy Fernandez.

“He’s been playing high-level basketball for such a long time,” Celtics center Neemias Queta said. “He understands tendencies, he understands how to make winning plays, understands how to play in a system. I think he’s only going to get better because he’s got his whole career ahead of him. He’s been big-time for us, and we’re going to need him to keep stepping up.”

Queta, a native of Portugal, said folks he knows at Real Madrid raved to him about Gonzalez’s on-court intensity after Boston drafted him in June.

“But it’s amazing to see it live in person,” the 7-footer added.

It didn’t take Gonzalez long to prove his skills could translate in the NBA. He played 22 minutes in the Celtics’ second game of the season, many of which he spent guarding New York Knicks All-Star point guard Jalen Brunson. A week later, he made a handful of hustle plays in a road win over the Philadelphia 76ers, including a full-court chasedown to deny a Quentin Grimes dunk that Queta said “was an epitome of how Hugo plays.”

“The main thing with him is just how hard he plays,” Queta said. “He doesn’t take any play off. … When you play that hard and you’ve got the intangibles — he’s got the IQ, as well; he’s got the length, the size — I think he’s got a bright future ahead of him. And it makes it so much easier for him when he’s got all that stuff together and the willingness to go out there and just do the dirty work. So he’s in a great spot.”

The Celtics have tapped into Gonzalez’s versatility, as well. For stretches against the Heat and Raptors, Mazzulla deployed him as an undersized five in smaller, more explosive lineups. Fellow youngsters Josh Minott (23 years old) and Jordan Walsh (21) also have played that role for Boston.

Gonzalez’s playing time has fluctuated this season, and he’s not immune to rookie mistakes. Before his back-to-back big nights over the weekend, he botched consecutive plays in a loss to the Detroit Pistons and got himself benched. Even in Saturday’s game, he picked up three first-half fouls against the Raptors, struggling at times to find the right balance between helpfully disruptive and unnecessarily aggressive.

But for a player who won’t turn 20 until February, the promise has outweighed the growing pains.

“He’s got a great knack for the ball defensively, and he’s learning how to play versus different matchups and coverages on the offensive end,” Mazzulla told reporters in Toronto. “The second half, he was great, and the last few games, he’s been great for us. So he’s just got to continue to get better and better.”