Morgan Geekie had a goal and two assists, Alex Steeves and Viktor Arvidsson each had a goal and an assist, and Elias Lindholm had three assists for the Bruins (16-13-0), who have alternated wins and losses in their past eight games (4-4-0). Mason Lohrei had two assists, and Joonas Korpisalo made 37 saves.
Pavel Buchnevich and Pius Suter scored for the Blues (9-12-7), who have scored two or fewer goals in nine of their past 10 games (3-4-3). Jordan Binnington, who was pulled in the first period of a 4-1 loss to the Anaheim Ducks on Monday, made 22 saves.
Steeves gave Boston a 1-0 lead at 6:30 of the first period. Following a bad line change by the Blues, Geekie skated in alone down the left wing before passing across to Steeves for a one-timer from low in the right circle.
Geekie then made it 2-0 at 11:25. Steeves won a wall battle below the goal line with Blues defensemen Colton Parayko and Philip Broberg, resulting in the puck popping out to Lindholm, who found Geekie in the low slot for another one-timer.
Buchnevich cut it to 2-1 at 1:59 of the second period. Parayko intercepted the puck along the right boards, curled around the net and found Buchnevich in the left circle for a one-timer.
Arvidsson responded to make it 3-1 at 6:04. Binnington steered aside a soft shot from Lohrei, but Arvidsson skated into the rebound near the right wall and beat the Blues goalie high on the short side with a slap shot.
Zacha pushed it to 4-1 at 12:26, cutting toward the high slot between two Blues defenders and roofing a shot over Binnington’s glove.
Zacha scored his second on the power play with 0.2 seconds remaining in the period. Lindholm collected a rebound near the left post and passed across the crease to Zacha, who buried the puck into the open net to make it 5-1.
Suter made it 5-2 at 9:07 of the third period. Korpisalo made a highlight-reel save with his right pad on Dylan Holloway, but the Blues forward got the rebound right back, circled the net, and passed out front to Suter.