Knicks forward Obi Toppin is fouled by Cavaliers forward Isaac...

Knicks forward Obi Toppin is fouled by Cavaliers forward Isaac Okoro as he attempts a dunk in the first half of an NBA game at Madison Square Garden on Saturday. Credit: Kathleen Malone-Van Dyke

RJ Barrett said Friday that spoiler can be “a fun role to play” and that the Knicks would aim to do just that in the five games they had left after being eliminated from playoff contention.

Then their first opportunity arrived on Saturday, and it proved to be no fun at all — a 119-101 loss to the Cavaliers at Madison Square Garden that even took the joy out of fan favorite Obi Toppin scoring a career-high 20 points.

“We lost today, so it doesn’t really mean anything to me right now,” Toppin said.

It was an important game for Cleveland (43-35), which solidified its hold on the seventh playoff seed in the Eastern Conference, which would secure a home game in the play-in tournament.

For the Knicks (34-44), it was another frustrating day at the office. “We didn’t come out with the edge and competitiveness that you need to win an NBA game,” Immanuel Quickley said.

Added coach Tom Thibodeau, “I think we were lethargic . . . You can deal with the missed shots, but defensively, we can’t win like that.”

Julius Randle sat out with a quadriceps injury, and Thibodeau said before the game that he is unlikely to return for the final week of the season.

That opens the door for others, including Toppin, who started on Saturday and was on a roll when he injured his left ankle and left the game in the third quarter.

He had 18 points at the time. He returned midway through the fourth quarter, still limping and with the Knicks getting blown out.

Had he talked his way back into the game, perhaps with an eye on that career high? Thibodeau and Toppin dismissed that notion. “My adrenaline was going,” Toppin said. “I felt good when I got back out there.”

Said Thibodeau, “The trainers make those decisions, so obviously we’re not going to put someone out there that’s injured.

“The player has input, but he’ll assess and then [the trainer] makes the determination whether the guy goes back in or not.”

For young players such as Toppin, this last week means a lot, even if it does not mean anything in the standings. The offseason will mean even more.

“I’m trying to work on everything,” he said. “Being a leader, working on my defense, working on ballhandling, every aspect of the game. I’m trying to dial in on this whole offseason.”

With the Knicks down to nine healthy players — Miles McBride sat out with a sore knee — Ryan Arcidiacono played 22 minutes, scored a season-high five points and added an assist. Before Saturday, he had played 17 minutes all season.

“He’s done a really good job in practice, so we want to see him out there,” Thibodeau said. “I thought he handled his minutes well.”

Darius Garland led the Cavaliers with 24 points and 13 assists. Former Net Caris LeVert added 19 points and Moses Brown, who played for Archbishop Molloy High School in Queens, had 16 points and 13 rebounds.

Evan Fournier scored 19 points and Quickley 17 for the Knicks. Barrett shot 4-for-18 from the field and scored 12 points.

The Knicks gave up 39 points in the first quarter, fell behind 68-60 at halftime and trailed by as many as 23 points in the second half.

The Cavaliers are a potential play-in opponent for the defense-challenged Nets.

“We’re a tough out for anybody,” coach B.J. Bickerstaff said. “Our strength is in our team, but when [Garland] is playing at his best, we’re extremely difficult to guard.”