Waltham, Mass. ? Maybe people who watched Boston chuck up all those three-pointers during the regular season got the wrong impression, but the Celtics have turned things around this season with defense, not offense.

“We are not the Dallas Mavericks. Nor are we the Sacramento Kings. … We aspire to that,” said coach Jim O’Brien, whose team faces Detroit today in Game 4 of the Eastern Conference semifinals.

The Celtics beat the Pistons, 66-64, Friday in the lowest-scoring NBA playoff game since the inception of the shot clock in 1955. The night before, the Kings and Mavericks were tied 66-66 at halftime.

“I would love to coach those high-powered, get out on the fast break offenses where our guys would run every night and score 130 points and win the NBA championship,” he said. “But we attempted to build this for the long term, and we started at the defensive end.”

Sixteen-time champions who hadn’t made the playoffs since 1995, the Celtics took almost 300 more three-pointers than the next highest team in the league during the regular season. Even so, they weren’t a high-scoring team, ranking 18th in the NBA in total points and ninth in points allowed; Detroit was 18th in points scored and sixth in points allowed.

O’Brien wants his players shoot three-pointers out of necessity, not choice, saying that his 49-win team would have had trouble winning 25 games in the regular season if they tried for points in the lane.

“For as long as I’ve studied basketball, the toughest defensive team has won championships,” he said. “That’s why we’re where we are, and that’s why Detroit is where it is.”