Murray is 5-1-2 in his past eight starts and has allowed two goals or fewer in five of those games. He was 5-5-0 in his previous 10 starts after winning nine straight from Dec. 15-Jan.11.
"We're down the stretch here, so every game is huge," Murray said. "It's basically playoff hockey from here on out, so [it] doesn't really matter who we're playing against. ... Every game is going to be like that."
Nick Bjugstad gave the Penguins a 1-0 lead on a wrist shot from outside of the crease at 1:33 of the first period before McCann made it 2-0 with a shorthanded goal at 13:54 of the first on a breakaway with a backhand shot.
"We were light on all the battles in the first," Bruins coach Bruce Cassidy said. "You could tell they were better prepared to win the pucks. It cost us a couple goals. Eventually, we got going. I thought the second period was good. We bounced back. ... That was a tough one to overcome against a hungry team with a pedigree."
Krejci made it 2-1 on a power play at 4:32 of the second period, but Jake Guentzel scored a power-play goal at 16:32 of the second to give the Penguins a 3-1 lead. It was Guentzel's 34th goal of the season.
John Moore got the Bruins back within a goal with Halak pulled at 18:59 of the third, but McCann scored an empty-net goal with 21 seconds remaining for the 4-2 final.
"I'm feeling more comfortable every game, it feels like," said McCann, who, along with Bjugstad, was acquired from the Florida Panthers on Feb. 1. "I'm playing with one of the best players in the world [first-line center Sidney Crosby] too, so that kind of helps. We created a lot tonight. ... I try to play good for the guys and not let them down."
