Jayson Tatum missed Saturday night's Game 7 for the Celtics with a leg/knee injury. (AP photo)

BOSTON (AP) — The Boston Celtics were reliving an NBA playoff nightmare on Saturday night.

Remember, they lost to the Miami Heat in the Eastern Conference semifinals three years ago when Jayson Tatum got injured in a Game 7.

They lost to the New York Knicks last year after losing Tatum to an Achilles injury in Game 4.

And Saturday night, they lost to the Philadelphia 76ers 109-100 in Game 7 of their first round Eastern Conference playoff series at TD Garden, again without Tatum. He was ruled out before the game with left knee stiffness.

The team announced the news about 90 minutes before the start of the winner-take-all first-round matchup.

“He just came in today with knee discomfort. The medical team and myself decided for him not to play,” coach Joe Mazzulla said during his pregame meeting with reporters.

With Tatum out, Mazzulla made radical changes to the starting lineup for Game 7, opting to start Baylor Scheierman, Luka Garza and Ron Harper Jr. alongside Jaylen Brown and Derrick White. It is the first time that group has started together this season.

Tatum averaged 23.3 points, 10.2 rebounds and 6.8 assists through the first six games of the series, while shooting 52.2% from the field and 36.5 from the 3-point line.

Tatum briefly left Game 6 in the third quarter for unspecified treatment of his calf. Tatum, of course, is just 22 games into his return from the torn right Achilles tendon injury he suffered in last season’s playoffs.

The Celtics downplayed the situation, with Tatum saying afterward that his leg was only feeling “a little stiff.” He said following a quick assessment and some time on the exercise bike he didn’t return because the game was out of hand and the starters had already been pulled.

But he was a late addition to the injury report on Saturday, listed first as questionable when the 1:45 p.m. report was released.

Tatum’s return to action was carefully managed during the regular season, beginning with a slow ramp up of his minutes. He also was not allowed to play in both games of a back-to-back.

But he’s had a lot less rest over the last three playoff games, playing every other night.

Saturday marked the 67th game this season that Tatum has not played.

This was the fifth time that the 76ers have played against Boston this season with Tatum sidelined.

“Obviously, it will change the matchups and things like that,” 76ers coach Nick Nurse said prior to the game. “Obviously, they played the majority of their season without him, and played very, very well. So, I think they’ve got enough games under their belt and have guys they trust and rely on and all that kind of stuff.”

The one postseason Tatum was healthy? That was two years ago, when the Celtics won the NBA championship.

(Telegraph Staff Writer Tom King contributed to this report.)