BOSTON - They started as a Big Three and grew to a Big Four when Rajon Rondo earned the right to be mentioned along with the other Boston Celtics All-Stars.

At no point, however, did Brandon Bass merit marquee billing in his first season in Boston.

The fifth, newest and least-heralded member of the Celtics' starting lineup, Bass erupted for a career playoff-high 27 points on Monday night, scoring 18 in the third quarter as Boston pulled away from the Philadelphia 76ers to win 101-85 and take a 3-2 lead in the Eastern Conference semifinals.

"We've got a few good players on the team that they had to focus on," said Bass, who left the game to a standing ovation with 2 minutes left and Boston leading by 18. "That left me open, and I was able to take advantage of my opportunity."

The 27 points matched Bass' regular-season career high, and the 18 points in the third was one off his career playoff high for an entire game. It was also more than the Sixers scored in the quarter as a team.

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"It was one of those games we needed something to ignite us together," Celtics coach Doc Rivers said. "I thought the biggest difference was his energy. He played with a force. I thought he just let himself go."

Kevin Garnett added 20 points and Rajon Rondo had 13 points and 14 assists for the Celtics, who can advance to the East finals with a victory in Philadelphia in Game 6 on Wednesday. The Sixers would need a win at home to force the series back to Boston for a decisive seventh game.

As he walked to his postgame interview, Elton Brand told the Celtics' ball boys in the hallway outside the locker rooms: "See you on Saturday."

No team has won consecutive games yet this series.

"It would just be nice to win two in a row. That would be terrific," Rivers said. "It's not going to be easy. This series has been hard. Every minute, you think we're leaking oil physically."

Brand scored 19 and Evan Turner had 11 points and 10 rebounds for Philadelphia, which led by six points early in the third quarter before Boston scored 14 of the next 16 points. Bass had eight of them, including back-to-back dunks followed by a steal that set up Ray Allen's fast-break layup to give the Celtics a 63-57 lead with five minutes left in the quarter.

Boston closed out the third with a 10-2 run over the final 3 minutes and outscored the Sixers 28-16 in the period. The Celtics also scored 16 of the first 22 points in the fourth quarter - seven from Rondo - to put away the game.

"We had too many turnovers and that just got those guys going," 76ers center Spencer Hawes said. "They got a couple of easy baskets in transition off our mistakes. It got them going, they took advantage of it and held home court. Now we have to go home and take care of ours."

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The Celtics acquired Bass in December in a trade with Orlando for Glen "Big Baby" Davis, and he worked his way into the starting lineup after the All-Star break. Although he solidified the power forward position after Garnett moved to center, he hadn't done anything spectacular - until Monday.

Bass hadn't scored more than 22 points in a game this season. His playoff high was 19 points, in 2008.

Paul Pierce had 16 points - a perfect 9 for 9 from the free throw line - and Allen, back in the starting lineup because of an injury to Avery Bradley, had five points.

Boston tied it 57-all when Bass stole the ball from Thaddeus Young and got to the free throw line, making both foul shots. After a Sixers miss, Rondo found Bass underneath for the dunk. Bass added another crowd-pleasing dunk before knocking loose a ball to start Rondo on a fast break he finished by finding Allen for the layup.

Notes: Actor Will Smith, a 76ers co-owner, was at the game, as were comedians Chris Rock and David Spade. ... Bradley did not play because of problems in both shoulders, Rivers said. ... Rondo had seven assists in the third quarter. He picked up one of his most spectacular when he slipped at the free throw line but left-handed the ball to Greg Stiemsma for the dunk.