Trent Frederic scored twice in 34 seconds in the third period, David Pastrnak had two goals, and Jeremy Swayman made 27 saves for the Bruins, who are 9-0-3 in their past 12 games.
"We just want to keep things rolling," Swayman said. "We know how good we are, and games like this, where you have a little adversity with travel or whatever, you want to get on top and get those two points. So, it's a feel-good win, but at the same time we're still not satisfied."
Pheonix Copley made 17 saves but had his seven-game winning streak end for the Kings (22-14-6).
"Obviously we just talked about how they capitalize on mistakes," Los Angeles coach Todd McLellan said. "We didn't make very many tonight, but they took advantage of the few that we made."
Frederic put Boston ahead 3-2 at 10:36 of the third, tipping in Brandon Carlo's shot from the right point, then made it 4-2 on a backhand from close range off Nick Foligno's pass from behind the net at 11:10 for his NHL career-high ninth goal of the season.
"I haven't had anything like that, like two goals in a shift," Frederic said. "I was actually ready to change after scoring the first one. Too much on the celebration. I was lucky enough, I stayed out there."