BOSTON — The biggest game of the Philadelphia 76ers’ season was Thursday night at TD Garden and Ben Simmons didn’t show up.

The likely NBA Rookie of the Year winner — sorry, Donovan Mitchell — scored just one point with five rebounds and seven assists in 31 minutes as Philly lost 108-103 to the Boston Celtics in Game 2 of their second-round NBA playoff series.

Simmons was a game-worst minus-23, missed all four shots he attempted and committed five turnovers. Not only was he ineffective as a scorer, he also wasn’t able to make a positive impact with his elite playmaking ability.

Simmons pointed to his own mistakes as the main reason for his lackluster performance.

“I think it was mainly what I did to myself,” Simmons said. “I think, mentally, I was thinking too much, over-thinking the plays. Wasn’t just out there, flowing, playing the way I play, which is free. I think, obviously, I know what their game plan is. I got to play my game.”

The Celtics have defended Simmons a lot like they contained Milwaukee Bucks star Giannis Antetokounmpo in the first round: by building a wall in the paint so the 76ers star is unable to penetrate to score or kick out for an open 3-pointer.

Everyone knows Simmons can’t shoot. He attempted 11 3-pointers all season and made zero. Teams often sag off him on the perimeter, but that usually just gives him a head start toward the rim and he normally uses his strength and athleticism to score at the basket.

Boston is preventing that penetration using the aforementioned wall and C’s defenders quickly moving their feet to cut off his drives to the basket. The Celtics also have a plethora of top-tier wing defenders who can switch any pick-and-roll, which helps prevent Simmons’ drives to the hoop.

“I think the way Boston is guarding us, in general, is something that I respect,” 76ers coach Brett Brown said. “I have said, every time either pre or post game, I have said this before, (the Celtics) are elite guarding their own men. I think there’s a physicality and switch-ability that they got apples for apples on many, many different matchups.

“With Ben, I give him credit. They do a good job defending him. There’s an element of physicality that I feel that they have applied to all of us and (Thursday night) Ben really struggled, as we see. I do give Boston’s defense a lot of credit and respect.”

Simmons didn’t start the fourth quarter with the 76ers trailing 79-75. TJ McConnell instead began the quarter as Philadelphia’s point guard, and deservedly so. He played really well off the bench and scored eight points on 4-for-4 shooting. Simmons entered the game with 5:29 left and Philadelphia up 93-91.

From that point, the Celtics closed the game on a 17-10 run.

Simmons hasn’t played well in this series, and that’s not a huge surprise because he’s a rookie, and the pressure of the playoffs is much more intense than during the regular season. But the 76ers cannot afford many more bad games from Simmons or a once-promising season could end in frustrating fashion.

“That’s the thing, I’m going to have bad games. It happens, obviously,” Simmons said. “It’s not the perfect timing, but we’re heading home now. We have two home games that we need to take care of and handle business.”

Thumbnail photo via Tim Fuller/USA TODAY Sports Images