The Milwaukee Bucks, ever so coolly and methodically, overcame a 17-point second-half deficit tonight and defeated the Boston Celtics, 95-91, at Boston Garden to take a 2-0 advantage in their best-of-seven NBA Eastern Conference semifinal playoff series.

The Bucks routed the Celtics by 21 points Wednesday in the first game here.

No team has ever won a seven-game series after losing the first two at home. The third and fourth games will be in Milwaukee Sunday and Monday.

"We still have to win two more," Milwaukee Coach Don Nelson said. "When we do that, it'll be over; not until then."

The Celtics, playing without star forward Larry Bird, who was home in bed with a 104-degree temperature, apparently because of influenza, played like a team possessed in the first half and appeared to have the game under control. But the Bucks never panicked or altered their game plan. When they needed baskets they patiently ran plays that isolated Junior Bridgeman, Sidney Moncrief or Marques Johnson against slower Celtics defenders.

It was a difficult driving layup by Moncrief, going to his left over 7-foot Robert Parish, that sealed the victory for the Bucks with 17 seconds left.

"I knew when I made the move there were only a few seconds left on the shot clock," Moncrief said. "I was kind of floating. I've made that shot before and I knew that even if I missed it, if I put it on the board soft enough, we had guys who could rebound it."

Moncrief scored 10 of his 20 points in the third period as the Bucks reduced a 59-42 Boston lead to 82-74 going into the final quarter. They then opened the last period with a 10-2 spurt, four of the points coming from Bridgeman, who finished with 19. Johnson tied the score at 84 with a twisting layup after he whizzed by Cedric Maxwell along the base line.

Scott Wedman's two baskets, around Johnson's dunk, put Boston ahead, 88-86, with 6:05 remaining, but the Celtics didn't score again until the 1:58 mark, and that came on Maxwell's technical foul shot after Milwaukee was caught playing an illegal defense.

During that spell, in which the Celtics missed five straight shots, Milwaukee scored six points. A free throw by Johnson followed by another by Bridgeman, after an illegal defense call against Boston, tied the score at 88.

Danny Ainge scored 23 points in the first half and and got his 25th point 13 seconds into the third period, but never scored again. He was on the bench resting as the Bucks were catching up, and the sellout Garden crowd of 15,320 was screaming for Coach Bill Fitch to put him back in the game, especially after Quinn Buckner missed badly on three straight jump shots.

With the score at 88-88, Ainge went back in and promptly missed a 15-footer. On the Bucks' next possession, Bob Lanier gave them their first lead of the night with a turnaround jumper, and after Ainge missed a 20-footer, Brian Winters made an 18-footer for a 92-88 Milwaukee lead with 2:14 remaining.

After Maxwell made his technical foul shot, the sides traded turnovers and missed shots until Parish tipped in Kevin McHale's miss to cut the lead to 92-91 with 37 seconds left.

Milwaukee, as it had done virtually all night, calmly worked the ball to the right person. Moncrief held it outside against Ainge until there were four seconds left on the 24-second clock and then he drove by him to the middle of the lane and jack-knifed a shot in over Parish with 17 seconds remaining.

Ainge took an errant three-point attempt and Lanier was fouled after he got the rebound and made one of two shots to seal the victory.

Boston, which shot 67 percent in the first half, missed 13 of its last 14 shots and scored only nine points in the fourth quarter.

The Celtics didn't miss Bird in the first half because Ainge and Wedman couldn't miss. Ainge, with the middle finger on his shooting hand heavily bandaged and taped to his ring finger (he was bitten by Tree Rollins Sunday), made 11 of his 12 shots, eight of them from 17 feet or further.

Milwaukee double-teamed whenever the ball went inside, which left Ainge open, and he kept making the shots.

McHale started for Bird, but went scoreless in the first half, so Fitch turned to Wedman, a 6-foot-7 jump shooter. Wedman made six straight shots, none from closer than 15 feet, and the Celtics cruised to a 57-42 halftime lead.

When the jumpers stopped falling, though, Boston had no Bird to turn to, and the Bucks took control of the game.

Bird is expected to play in the third game Sunday.