Vladimir Tarasenko scored twice and Alex Steen added three assists as St. Louis used a second-period surge to take down struggling Boston by a 5-1 count at Scottrade Center.
Alex Pietrangelo, Petteri Lindbohm and T.J. Oshie also connected for the Blues, winners in four of their last five games.
Jaden Schwartz collected a pair of helpers and Jake Allen stopped 26 shots.
Brad Marchand picked up the lone goal for the Bruins, whose season-high losing streak reached six straight games (0-4-2).
“I felt we were moving the puck well … Around the net, we don’t seem to be burying those,” Boston coach Claude Julien said.
Malcolm Subban’s NHL debut lasted just over half of regulation. He yielded three goals on six shots in the opening 25 minutes, then did not face a shot over the final six-plus minutes in regulation. Tuukka Rask spelled him, giving up a pair of goals on nine shots.
St. Louis moved quickly to score three straight on three shots in the early part of the second.
Lindbohm scored his first NHL goal on a long shot during 4-on-4 play at 48 seconds, Pietrangelo put the hosts ahead from the left circle at 4:16 and Oshie chased Subban with a blast from the right circle at 5:09.
“What doesn’t kill you makes you stronger, so you’ve just got to take that approach to tomorrow, and the day after,” Subban said.
Tarasenko beat Rask on the advantage to make it 4-1 at 13:59 and then scored on a fluttering shot from below the circles at even strength with 8:15 left in the third.
“He’s extremely lethal. As soon as he gets a chance there’s a pretty good chance it’s going to end up in the back of net,” Steen said of Tarasenko’s skill level.
Marchand’s shot off a rush up the left wing fell from Allen’s glove and into the net just after the midway point of the first period.