Al Horford was content to take on a supporting role for the talent-rich Celtics in his 17th NBA season.

But on Wednesday, the 37-year-old big man took his turn in the spotlight to help power Boston to the Eastern Conference finals.

Horford’s stat line in Boston’s 113-89 win over Cleveland: 35 minutes, 22 points, 6-for-13 from 3-point range, 15 rebounds, five assists, three blocks, one steal.

He became the first player in NBA postseason history to rack up 20 points, 15 boards, five threes and three blocks in a single game. He’s the third-oldest to notch a 20-point, 15-rebound, five-assist playoff game, trailing only LeBron James and Kareem Abdul-Jabbar.

Horford’s reaction to those historic achievements?

“It feels great because we won,” the veteran center said, smiling. “That’s the only satisfaction I get out of it.”

And even on a night like this, some of Horford’s greatest contributions didn’t show on the stat sheet. He challenged teammates during timeouts. He vaulted out of bounds to save a loose ball and prevent a turnover. He was ferocious on the glass, grabbing more offensive rebounds (seven) than all of Cleveland’s roster combined.

“For me, the biggest thing was just bringing energy — bringing energy to our group,” Horford said. “I felt like we lacked it the first quarter, and when I came back in the second, I felt like we needed to step it up. We were talking about it a lot in the huddle, but we weren’t really getting it done.”

Despite missing three key players in Donovan Mitchell, Jarrett Allen and Caris LeVert, the Cavs fought hard to extend their season, trailing by as little as three early in the fourth quarter. Horford’s late-game contributions were pivotal for Boston.

In the fourth quarter alone, Horford vacuumed up nine rebounds, scored eight points and drilled two threes as the Celtics pulled away for a comfortable win. After his final 3-pointer put Boston up 17 with less than a minute remaining, he left the court to a standing ovation.

“His performance, his energy, his leadership tonight was crucial,” Jayson Tatum said.

ECF schedule still TBD

Boston Celtics guard Derrick White, left, has the ball knocked away by New York Knicks guard Donte DiVincenzo during NBA action Thursday at the TD Garden. (Staff Photo/Stuart Cahill/Boston Herald)

The Celtics will face either the Knicks or Pacers in the East finals, but that series still is ongoing. New York leads 3-2, with Game 6 set for Friday night in Indiana.

If the Knicks close out the Pacers in six games and the Denver Nuggets do the same to the Minnesota Timberwolves in the West, then Game 1 of Celtics-Knicks would be Sunday at 1 p.m. at TD Garden. If either of those series reaches Game 7, Boston’s next game would be next Tuesday night against New York or Indiana.

That means the Celtics will have either three or five days to rest after this latest series win.

“It’s important to take advantage of the opportunities that you have,” head coach Joe Mazzulla said. “It’s a gift that we’ve got the rest now because we took advantage of the opportunity that we have. We can be grateful for that rest, but you don’t know. Sometimes rest isn’t good for you; sometimes it is. We’ll at least take (Thursday) off.”

This is Boston’s third consecutive Eastern Conference finals appearance and its sixth in the last eight seasons.

It remains to be seen whether Kristaps Porzingis, who missed the entire East semis with a calf strain, will be healthy enough to return for the start of the conference finals. But Boston’s layoff can only help the big man’s recovery timeline.

HC Cassell?

Sam Cassell shown in 2021 when he was an assistant coach for the Philadelphia 76ers. (AP Photo/David Zalubowski)

The Celtics already are preparing to lose one assistant coach after their playoff run concludes. Now, another is drawing interest as a head-coaching candidate.

The Los Angeles Lakers received permission to interview Sam Cassell for their top job after firing Darvin Ham earlier this month, per ESPN.

The well-traveled Cassell played for eight teams — including the Celtics — during a 15-year NBA playing career, and he now is in his 15th season as an assistant coach.

Mazzulla hired Cassell to his Celtics staff last offseason and spoke glowingly about the 54-year-old on Wednesday.

“He’s been in every seat on the bench in the NBA, so he knows how to communicate with every single player because he’s been where that particular player has been,” Mazzulla said in his pregame news conference.

“One of the first things he does when we get on the plane is he watches film. Even though he’s a former player, he’s a guy that wants to study the game. He’s loyal, communicates well. He’s a good coach — great coach. I’m happy to have him.”

Related Articles

Callahan: The Celtics’ playoff run has been easy and boring. Enjoy it

Celtics topple Cavaliers in Game 5, advance to Eastern Conference finals

Celtics happy to clinch first close win of playoffs: ‘We kind of wanted it’

Jayson Tatum, Celtics survive short-handed Cavs in Game 4, take 3-1 series lead

Celtics catch major break with Cavs’ Donovan Mitchell out for Game 4

Mazzulla’s top assistant, Charles Lee, was hired last week as the Charlotte Hornets’ next head coach. Lee will remain with Boston through the rest of the playoffs.

Others linked to the vacant Lakers job are Pelicans assistant James Borrego, Timberwolves assistant Micah Nori, Nuggets assistant David Adelman and NBA player-turned-analyst J.J. Redick.

Off the rim

Among those in attendance at Game 5: Christian Gonzalez. The young Patriots cornerback wasn’t the biggest celebrity in the crowd, however. That honor went to Russell Wilson and Ciara, who were seated next to Cleveland’s bench. … Cavs guard Max Strus arrived at TD Garden wearing a Florida Panthers jersey, an apparent reference to the NHL club’s comeback from a 3-1 series deficit against the Bruins last postseason. Strus finished with 12 points in 45 minutes as his team failed to replicate that feat.