Boris Katchouk had a goal and two assists, and Petr Mrazek made 16 saves for the Blackhawks (23-38-6) before he left the game at 8:48 of the second period. He had made two saves against Trent Frederic before a shot by Dmitry Orlov at 7:47 knocked Mrazek's mask off his head. He was replaced by Alex Stalock, who allowed three goals on 26 shots for the win.
Chicago coach Luke Richardson said Mrazek left with a groin injury, which has been an issue in the past.
"Very similar injury to earlier in the year, but not as severe," Richardson said. "So, that's good news. But we'll have to reevaluate him tomorrow morning and get him checked out properly. As of now, he's probably not going to start the [upcoming five-game] trip with us, but they think he'll probably join us on the trip, so that's the good news.
"Doesn't seem to be as bad, they said, so I think they just said he pulled himself because he knows it could get worse if he stayed in. It could have been really bad, so I think it was a smart call to get him out. Of course, Alex is the type of goalie that can go into a situation like that, the way his play is and his manners, he can handle that situation, so it worked out well."
Hampus Lindholm had a goal and an assist, and Linus Ullmark made 23 saves in his first loss since Jan. 29 for the Bruins (50-11-5), who have lost three of four. Boston has a 17-point lead on the second-place Toronto Maple Leafs in the Atlantic Division.
"You get humbled in this league if you don't put on your work boots and don't come to play together as a team," Bruins coach Jim Montgomery said. "That mental focus has been there. Now it's two stretches that we haven't had it. First one, I thought it was physical fatigue. This one, there's no reason for physical fatigue, and we look like we're tired."