Boston’s Jaylen Brown puts up a shot Thursday against the Los Angeles Lakers in Los Angeles. Ringo H.W. Chiu/Associated Press

Celtics All-Star guard Jaylen Brown is growing right before everyone’s eyes – and this season is just the latest in his transformation.

Brown put up 40 points – his third career 40-point game, all this season – on an efficient 17-for-20 shooting performance on Thursday night, boosting the Celtics to a 121-113 win over the Lakers at Staples Center that capped a 3-0 road trip.

No more is Brown that fresh, college-aged kid who needed to work on his dribbling, playmaking and nearly every facet of the game. He’s improved at least one part of his game every offseason, and the scoring has followed, with Brown averaging 24.6 points per game this year.

“Just wanted to come and be aggressive,” Brown said of his game. “Celtics-Lakers matchup is a matchup that kids dream about. They know who’s on the floor. Regardless of who was on the court, I’m excited to play. That energy, having those Lakers fans back in the arena. We just wanted to come out and get a win.”

It was another night where the Celtics handed off who led the way. While fellow All-Star Jayson Tatum had a quiet night with 14 points, it was Brown’s turn to be the best player on the court, and he was crucial in the win as he finished a staggering plus-36 in his 32 minutes played.

The Boston bench struggled in its first stint of the game Thursday, which allowed the Lakers to chip away at a big deficit to make it a somewhat-competitive game. While the Celtics built their lead by halftime, Coach Brad Stevens still elected for a change.

Stevens threw out Brown and the Boston bench mob in the third quarter and the Celtics went on a huge run, stretching a lead that hovered around a dozen all the way to 20, which should have put the game away. But Boston’s third-string players almost blew a 27-point lead in the last seven minutes, forcing the starters back in.

Stevens emptied his bench with about nine minutes remaining, but the huge lead was cut to five before Brown re-entered and made two late basket to secure the win.

There are still some areas of Brown’s game he can work on. His assists have been down and he’s struggled against physical defenses. But that’s all a process – one that Brown has shown he’s working on throughout his young career.

“Just an elevated responsibility,” Brown said of what’s different this season. “I’m in more of a role to play-make and things like that than I’ve ever had. It’s a big piece, but just studying and watching the game and improving. That’s what I’m all about.”

THE CELTICS signed Jabari Parker to a two-year contract in hopes of unearthing the talent that once made NBA evaluators predict stardom for the former Duke star.

Shams Charania of The Athletic and Stadium reported the move.

Parker, 26, was the No. 2 overall pick by the Milwaukee Bucks in the 2014 draft. He last played for the Sacramento Kings on March 15, but appeared in only three game this season and was waived on March 25.

The 6-foot-8 power forward suffered a torn ACL twice in the first three seasons of his career and never blossomed into the player people expected after he left Duke. But he’s averaged 14.8 points per game in his career, which has had stops in Atlanta, Washington and Chicago. His best season was 2016-17, when he averaged 20.1 points and 6.2 rebounds for the Bucks.

Charania later tweeted that the Celtics are cutting Moe Wagner to make room for Parker.

RISE IN STANDINGS: A five-game winning streak this late in the season does wonders in the tight Eastern Conference standings. But that doesn’t mean the Celtics are in the clear, even though Boston is now tied with Atlanta for fourth at 30-26. Keep in mind that the resurgent Hawks have the tiebreaker over the Celtics.

There’s still not much room for mistakes. The Celtics are only one game above the sixth-place Knicks, 1.5 games ahead of the Heat and two games ahead of the Hornets. It’s still packed, and a few losses could see the Celtics right back in the middle of the conference.

FANS IN THE BUILDING: Playing basketball during the pandemic means, at the very least, teams are playing in front of sparse crowds, not nearly close to capacity. Players and coaches have gotten used to it, though fans are finally back at venues like the TD Garden on a limited basis.

There are caveats to that, Stevens said, especially in big games like Celtics-Lakers. California recently opened up some events at indoor venues, which allowed Los Angeles to open Staples Center to fans for the first time Thursday – just in time to watch one of the best rivalries in the NBA.

Stevens said in pregame he was glad fans were back in the stands (even if the Celtics were showered with boos). In the first meeting in Boston, Stevens said the empty stadium felt “eerie.” Despite getting used to performing in front of crowdless arenas, Stevens said there was a heightened strangeness for such a normally high-stakes game.

“I think we played 75 games before we had fans back in Boston, whether it was the in the bubble or at home,” Stevens said. “But there was one that stood out above all others, and how eerie it felt, and that was the Lakers game. … This thing was meant for people to be here.”

ROOKIE PAINS: Rookie point guard Payton Pritchard burst onto the scene this season, quieting the critics who questioned why the Celtics took him late in the first round. He was getting a lot of playing time with Kemba Walker out, shooting lights out, and even made a game-winner against the Heat.

The hype has dialed back significantly while his play quality has been sporadic. Pritchard finished with a solid 15 points on 5-for-11 shooting while adding seven rebounds and three assists Thursday. It was the first time he broke the 20-minute mark since March 27, a win over Oklahoma City.

It’s been a grind of late for Pritchard. In his homecoming game against Portland, he shot 1 for 7 in limited minutes. Coming into Thursday’s game, he was averaging only 13 minutes per game in April, the lowest of any month in his rookie season. That’s all a process, Pritchard said.

“You could probably say something like that,” Pritchard said of hitting a rookie wall. “It’s a grind and it’s my first time going through it, so it’s a learning experience. So, your body gets tired, you get mentally tired, so finding ways to get through that and staying sharp will benefit me in the future.”