ATLANTA — The Hawks held the Boston Celtics to the lowest-scoring first quarter in the playoffs since the NBA went to the shot clock, building a 21-point lead and holding on despite an ugly shooting performance of their own for an 89-72 victory Tuesday night, giving Atlanta a 2-0 lead in the opening-round series.

Al Horford and Kyle Korver led Atlanta with 17 points apiece, but this game was essentially decided in the first 12 minutes.

The short-handed Celtics turned in the lowest-scoring first quarter in an NBA playoff game since the league went to a shot clock in 1954, managing just seven points.

Playing without two key players, Boston made just 3 of 23 shots from the field and missed all six attempts beyond the 3-point arc.

Celtics star Isaiah Thomas went 1 of 6. Marcus Smart, starting in place of the injured Avery Bradley, missed all five of his shots. Evan Turner and Tyler Zeller each went 0 for 3. The Hawks made things especially tough from close in, blocking six shots.

According to STATS, the previous record for fewest points in an opening quarter during the shot-clock era was eight, initially set by Utah in a 1988 game against the Los Angeles Lakers and matched by Dallas in a 2010 game at San Antonio.

It was also Boston’s lowest-scoring playoff quarter since the NBA was founded in 1949. The team made one playoff appearance in the league’s predecessor, the Basketball Association of America (BAA), but records from that series were not available.

In addition to Bradley being out, likely for the rest of the series with a severe hamstring injury, the Celtics played without Kelly Olynyk, who was sidelined with a shoulder injury. That cost Boston two of the six players who averaged in double figures during the regular season.

It sure showed.

The Hawks matched their franchise record for the fewest points allowed in any playoff quarter. They also surrendered seven in the fourth period of a 90-64 win over the Miami Heat in 2009.

Atlanta failed to score over the final 5:28 of the period and still led 24-7.

Game 3 is Friday night in Boston.