David Pastrnak scored, and Jeremy Swayman made 17 saves for Boston (38-14-15), which had its four-game point streak end (3-0-1).
“I didn’t like our start,” Bruins coach Jim Montgomery said. “I didn’t think we had the intensity that’s required in this league to start games on time. ... We created a lot of good scoring chances. We missed the net, they blocked shots. Their desperation probably was, defensively, a little bit higher than ours.”
Kapanen gave the Blues a 1-0 lead at 10:13 of the first period. Torey Krug's attempted pass around the boards caromed off a stanchion into the low slot, where Kapanen beat Swayman blocker side.
“It was just going in today,” Kapanen said. “Just happy to see. I feel like it hasn’t really been bouncing, necessarily, the way I wanted this year, so just having a game like this, it really feels good.”
Robert Thomas made it 2-0 at 17:59, taking a return pass from Pavel Buchnevich and scoring with a one-timer from the top of the right circle during a 5-on-3 power play. It was his 21st goal of the season, an NHL career high.