Unable to blow out or shake off the Milwaukee Bucks tonight, the Boston Celtics nevertheless never trailed and moved to a 2-0 lead in the best-of-seven NBA Eastern Conference finals with a 122-111 victory. Game 3 will be played Saturday afternoon at the Mecca in Milwaukee.

Accustomed to early dominance in the Celtics' last two home games, the crowd of 14,890 -- the 267th consecutive sellout at Boston Garden -- stirred uncomfortably as the Bucks scored nine consecutive points midway through the fourth quarter to cut a 99-86 lead to 99-95 with a little more than six minutes left.

From that point, however, the Celtics' deeper talent began to wear on the Bucks. Robert Parish scored four quick points, Kevin McHale added a pair of three-point plays and Boston pulled away.

"There's a confidence that this team has," said reserve center Bill Walton. "Maybe it's from being together all year and watching people like Larry Bird and Robert Parish and Dennis Johnson making great plays over and over."

Bird led all scorers with 26 points, and every other Boston starter joined him with at least 20. Milwaukee was led by Terry Cummings with 23 points. Bucks centers Alton Lister and Randy Breuer scored career playoff highs with 22 and 21 points, respectively.

Their output was a marked contrast to their Game 1 performance, in which Lister and Breuer combined for but 17 points. Then again, the entire Milwaukee team was greatly improved, shooting 56 percent from the field for the game after a sickly 38 percent in the series opener.

Although sixth man Ricky Pierce was unable to play because of a sore shoulder, the Bucks benefited from the return of Sidney Moncrief, the all-star guard with the nagging left foot injury, to the starting lineup. Add that the game was being played on Milwaukee Coach Don Nelson's 46th birthday, and that he also became a grandfather earlier in the afternoon, and one would believe things boded well for the Bucks.

However, it was all overridden by what has come to be known as the Celtics' mystique, an inexplicable element of luck that has gotten them out of more than one tight spot through the years.

Tonight it began shortly after the Bucks (down 36-29, 63-55 and 89-80 at the quarters) had closed to 99-95. Twice, with the 24-second clock running down to less than five seconds, Moncrief blocked Boston shots, just failing to retrieve the loose balls. Just before the clock expired a third time, Moncrief was whistled for a foul, with Parish scoring a short time later.

The killer came with 2:45 to play. Boston guard Danny Ainge bounced the ball off his foot and seemingly out of bounds. Making a mad lunge, however, he was able to flick it toward midcourt, where it hit Bird, who quickly passed it to Kevin McHale. McHale scored on a short shot and, fouled on the play, added a free throw. That made the score 110-101 and the Bucks would get no closer than seven points the rest of the way.

"We got the ball where we wanted to, we scored whenever we wanted to and we still lost," said Cummings. "You can't pinpoint where or when but the crazy things started happening."

Until then, the Bucks were able to stay in the game -- although Moncrief scored only two points in 37 minutes -- not only because of their improved offense but also through a defensive wrinkle.

In the series opener, Milwaukee seemed content to try to play Boston's taller, more talented players man-to-man but were repeatedly burned. Tonight, whenever Bird, McHale, Parish or Walton touched the ball in the low post they were immediately double-teamed by either a guard or a forward.

The ploy served two purposes, but one worked in the Celtics' favor. First, it clogged the middle of the lane, reducing the Celtics' ability to power their way to the basket. Second, it forced Boston to move the ball about the perimeter either with a long diagonal toss or a series of whippetlike passes. That has been one of the Celtics' strengths all season and it was no different in the early going tonight, as Ainge and Dennis Johnson scored repeatedly from the outside.

"Yeah, they double-teamed from all over the place tonight," said McHale. "One time I looked up and I had three guys coming after me. I just wanted to get rid of the ball and hide. I felt like Custer and the Indians were coming after me."

In the first quarter, Johnson carried the outside shooting to an extreme. Trying to throw a lead pass to Bird from his own three-point circle, the guard saw his long, arcing toss nestle into the basket for three points from 70 feet away.

"I practice that all the time but I never make 'em," he said. Although he didn't attempt any other long hoists, during the second half Johnson had a tougher time making baskets from closer in, hitting on just two of six shots. When the other Celtics began to experience similar difficulties, it gave Milwaukee a chance to make things interesting.

In the end, though, Boston had run its 1985-86 home record to 47-1. Small wonder the club was able to announce tonight that Parish, a six-year Celtic who could have become a free agent after the playoffs, had signed a multiyear renewal.