Larry Bird scored 35 points, including the basket that put Boston ahead to stay with 39 seconds left, as the Celtics mastered the Bulls in Chicago yesterday, 109-103, for a 4-0 sweep of their NBA Eastern Conference semi-final.

Boston, having attached the four victories to the league's best regular-season record, advanced to the conference final series against the Milwaukee-Philadelphia survivor.

Boston trailed, 103-102, when Bird took the lead away from the Bulls. Chicago called time to plot strategy for its ensuing possesion, but Dwight Jones' shot missed and, with the Bulls forced to foul, Cedric Maxwell made one of two free throws and Boston got the rebound.

Bird was fouled and made two free throws with seven seconds left. Bird tossed in two more shots with :001 left and the Celtics had scored the game's final seven points.

It was 80-80 entering the fourth quarter. Bird hit a three-point basket and layup in the opening minute to give Boston an 85-80 lead.

Ricky Sobers, who scored 17 points, rallied Chicago to 91-all midway through the quarter. Boston came back to take a 98-93 lead with four minutes left. Chicago outscored the Celtics, 10-4, in the next three minutes and went up, 103-102, with two free throws by Reggie Theus.

Nate Archibald and Kevin McHale had 14 points each for Boston. David Greenwood scored 24 for Chicago.