When LeBron James was asked after the Los Angeles Lakers’ loss Tuesday in Atlanta what he was going to tell his teammates ahead of critical matchups against the Boston Celtics and New York Knicks, he had a simple response.

“Just go out and do your job,” James said.

Message received.

With James (left ankle peroneal tendinopath) and Anthony Davis (bilateral Achilles tendinopathy and left hip spasm) ruled out five hours before tipoff, the shorthanded Lakers stunned the full-strength Celtics 113-105 at TD Garden on Thursday night.

The victory was perhaps the Lakers’ best of the season.

The Celtics were an NBA-best 37-11 and 22-2 at home. Even if James and Davis had been available, the Celtics were going to be heavy favorites. Without the duo, logic suggested that the middling Lakers had no shot.

But behind a season-high 32 points from Austin Reaves (including a career-high seven 3-pointers), a near triple-double from D’Angelo Russell (16 points, eight rebounds and a season-high 14 assists), an inspired effort from their remaining frontcourt players and a scorching 3-point shooting performance (19 of 36, 52.8 percent), the Lakers pulled off the stunning upset.

“We’re all talented players,” Reaves said. “And this is an opportunity to show the world what you can do. … So before the game, we come together and were like, ‘Look, the least we can do is we can go out there and play as hard as we can and live with the results.’”

The results were shocking considering the Lakers’ previous two performances. They were blown out in Houston with James and Davis available (though Davis was hobbled in the second half due to hip spasms) and blown out again in Atlanta with just James. They lost to the Celtics by 11 points on Christmas Day at home, despite James and Davis playing.

This was the first game this season that both stars missed together. They participated in Thursday’s shootaround before the medical staff ruled them out. The buzz surrounding the nationally televised game was wiped out midday, replaced by expectations of  a Celtics rout.

But without their two offensive fulcrums, the Lakers played a freer offensive style, with a steady dose of Reaves and Russell pick-and-rolls leading into quick-hitting actions on the opposite side of the floor. The Lakers trailed just once after the first quarter. The Celtics never got closer than seven points in the fourth.

 

Reaves’ best offensive performance of the season came one game after he produced his then-season-high against Atlanta (28 points on 10-of-19 shooting). His seven 3-pointers set the tone against Boston, with him routinely stepping into 3s in pick-and-rolls or dancing with Celtics defenders to create separation for step-back attempts.

Lakers head coach Darvin Ham said he spoke with Reaves on Wednesday and thanked him for “what he’s meant to our program.”

“Just his scrappiness, his willingness to lay it on the line. He’s been nothing short of amazing since he’s been in a Laker uniform,” said Ham. “And specifically, since I’ve been here as the head coach, he’s laid it on the line every single time. You can trust him at big moments and he’s gonna do his part.”

While Reaves paced the offense, with notable contributions from Russell and Rui Hachimura (15 points), the defense was led by Jarred Vanderbilt and Jaxson Hayes, who used their length, athleticism and energy to disrupt Boston’s second-ranked offense.

Hayes (16 points, 10 rebounds and three steals) played his best game since signing with the Lakers over the summer, following four seasons with the New Orleans Pelicans. He set season highs in points, rebounds and minutes (34). It was his first double-double as a Laker and first in nearly two years.

As Hayes returned to the locker room after speaking with the media, Davis, who was the headliner of a 2019 trade that eventually took Hayes to New Orleans, greeted him with a reference to their former team.

“Yeah, Baby Shaq!” Davis said. “Yeah, Baby Shaq, let ’em know! This ain’t New Orleans.”

This was also the first time this season in which Hayes played double-digit minutes without fouling.

“He’s learning,” Ham said. “And him getting these real game reps has been priceless. He has so many times where he showed his hands. …(Jayson) Tatum was working his way downhill, Jaxson was moving his feet and just showing his hands. And earlier in the season, we’ve seen him come out with three, four fouls quick. It just shows the growth that’s in him and the reason why he’s here.”

Hayes said he’s been going through individual drills to work on not showing his hands or fouling. In one, three coaches drive at him and he contests their shots using verticality. In another, he contests pump-fakes, doing his best to stay down.

“That was a big talking point for coach (Ham) on why I was taken out of the rotation earlier in the year,” Hayes said. “So I just wanted to make sure I did a good job on it today.”

Vanderbilt (10 points, seven rebounds and three steals) is having the best scoring stretch in his career, with six double-digit point totals in his past eight games. He also limited Tatum in their one-on-one matchup while also disrupting passing lanes and covering for his teammates. Per NBA.com player tracking data, Tatum has scored just five points on 1-of-3 shooting to go along with two assists and one turnover in the six and a half minutes Vanderbilt has defended him in two matchups this season.

Vanderbilt exited the game for good late in the first half after stealing the ball from Tatum and stepping awkwardly with his right foot. X-rays were negative. Vanderbilt also has been dealing with left heel bursitis since training camp, which has kept him out of 21 games.

“It’s a shame he went down, but shout out to Vando,” Ham said. (He) set an unbelievable tone for the game. His scrappiness, guarding everybody, starting on Tatum, of course, rebounding, getting us extra possessions, steals. Made some great passes, gave us a couple assists. So he was great.”

If Vanderbilt misses any time, he’d join Cam Reddish (right ankle sprain) and Gabe Vincent (left knee surgery) as notables on the injury report. James and Davis are day-to-day heading into Saturday’s game against the Knicks. Davis, who was announced as a West All-Star reserve before the game, spoke at shootaround and said he was feeling better.

Going forward, the Lakers must figure out how to channel Thursday’s offensive aggression into games in which both James and Davis play.

“I just think they can’t be paralyzed mentally in thinking they gotta do things to get Bron and AD the ball, their touches, (getting them) going,” Ham said. “Those two guys are great. They’re All-Stars for a reason. They’ve been who they are throughout the course of both of their careers for a reason. But they’re also two guys who want people around them to play the right way and make the right play when it’s in front of them. … To be in attack mode constantly and also defensively to be where they’re supposed to be.”

Russell, meanwhile, offered an explanation for the team’s spirit and mentality.

“I think that’s trust,” Russell said. “If you miss shots and you’re subbed out, how are you gonna feel about that? You’re gonna feel some type of the way. I think as a coaching staff around the league, around all professions, they’re successful when they recognize their players are kind of getting lost in the sauce and they find a way to give them some love or find a way to get them something easy. You know?

“I think when you get that trust from your coach, it allows everybody, one through 15, to go out there and impact winning. They don’t care. They know turnover, missed three shots in a row, get blown on defense, you still have trust within the group.”