The Portland Trail Blazers capitalized on an injury to Victor Wembanyama to pull off a 106-103 upset over the second-seeded San Antonio Spurs on Tuesday, tightening their Western Conference playoff series.

San Antonio superstar Wembanyama – who had scored 35 points in the Spurs' game one win Sunday – exited in the second quarter at the Frost Bank Center in Texas after hitting his head on the court following a collision with Portland's Jrue Holiday.

The 22-year-old looked groggy as he lay on the floor for several minutes before getting to his feet and jogging to the locker room.

The 2.24-meter forward was subsequently ruled out of the remainder of the game after entering the concussion protocol.

San Antonio looked to have overcome Wembanyama's injury as they pulled into a 14-point lead early in the fourth quarter, leading 93-79 with just over eight minutes left on the clock.

But with victory seemingly in sight, San Antonio's shooting went ice cold and the absence of newly crowned NBA defensive player of the year Wembanyama was keenly felt as a determined Portland snaffled victory, closing the fourth quarter with a 27-10 run.

Scoot Henderson led Portland's scoring with 31 points, while Holiday added 16.

"Basketball is a game of runs, and the basketball gods are always gonna repay the ones that play the game right," Henderson told NBC television afterwards.

Game three of the best-of-seven series takes place in Portland on Friday.

In the Eastern Conference playoffs, Tyrese Maxey and VJ Edgecombe combined for 59 points as the Philadelphia 76ers scored a series-leveling 111-97 victory on the road over the Boston Celtics.

Edgecombe made six-of-10 3-point attempts before finishing with 30 points, 10 rebounds and two assists in a stunning victory for the Sixers, who had trailed 26-13 early in the first quarter before rallying.

Maxey was also lethal from long-range, making five 3-pointers on his way to a 29-point haul.

The bounce-back victory came after the Sixers were thrashed 123-91 in game one Sunday, after a performance that Philadelphia coach Nick Nurse lambasted as "absolutely unacceptable."

Nurse was unsurprisingly happier with his team's winning display Tuesday.

"I thought we just played much better team defense tonight," said Nurse, who also saluted his team's resolve after Boston surged into an early double-digit lead.

"I think we did a great job of just taking that punch," Nurse said.

"They were spectacular to start, but we just hung in there. I said 'Listen, they're pretty great right now, let's believe that they're not going to be this great the whole game, and just hang in there'. And our guys did."

Jaylen Brown led Boston's scoring with 36 points, but Jayson Tatum was the only other Celtics player to make double figures with 19 points. The Celtics made just 35-of-89 shots from the field throughout the game.

"You have to be able to score in close games against a team like that," Celtics head coach Joe Mazzulla said. "They made more shots than us down the stretch."

With the series knotted at 1-1, game three takes place in Philadelphia Friday.