With Jayson Tatum out, Celtics debut brand-new starting lineup in Game 7

With Jayson Tatum unavailable, Celtics head coach Joe Mazzulla threw his starting lineup into a blender for Game 7 against the Philadelphia 76ers.

Boston opened Saturday’s win-or-go-home game at TD Garden with a five-man unit of Derrick White, Ron Harper Jr., Baylor Scheierman, Jaylen Brown and Luka Garza.

White and Brown are longtime starting-lineup staples, and Scheierman, Harper and Garza all started games at different points this season. But this was that quintet’s first time sharing the floor. They’d played zero minutes together during the regular season or postseason.

Harper, Scheierman and Garza were part of Boston’s top-performing lineup in Game 6. Those three, along with Payton Pritchard and Jordan Walsh, staged a late-game rally, cutting a 23-point deficit to 12 before losing steam in the final minutes of Philadelphia’s series-extending 106-93 win.

The trio of new additions also played key roles in one of the Celtics’ most memorable wins of the season: the Game 82 matchup with the Orlando Magic that Boston won despite sitting their top seven rotation players. Harper, Scheierman and Garza combined for 84 points in that win, with Garza hitting the decisive 3-pointer late in the fourth quarter.

Scheierman and Garza have seen sporadic playing time in Boston’s first-round playoff series, but Harper — who only had his two-way contract converted to a standard deal last month — had only played in blowouts before his surprise start on Saturday.

The radical lineup change pushed usual starters Neemias Queta and Sam Hauser to the bench. Queta had started 81 of the 82 games he’d played this season, including each of the first six playoff games, but he’s struggled to stay out of foul trouble against the Sixers. The Celtics were outscored with Hauser on the floor in four of the first six postseason contests.

Mazzulla opted for Garza over veteran center Nikola Vucevic, who has been Queta’s primary backup when healthy.

Tatum was ruled out for Game 7 with left knee tightness.