An innocent looking play led to the Flames next goal, with Gaudreau literally Johnny on the Spot after Noah Hanifin took a sharp-angle shot from down low and Sean Monahan swept the rebound across the crease with one hand to No. 13, who calmly tapped it home with less than five minutes to play in the period.
Just 48 seconds later, Valimaki - the Flames 2017 first-round pick - faked a big slapshot and froze Noel Acciari near the blue-line and then took three of four strides toward the net before firing a high shot from the left faceoff circle that Rask got a piece of but it went up and over his head and dropped to the ice and slid across the goal-line.
The Bruins appeared to have tied things up with 2:43 remaining in the first, after Pastrnak one-timed a cross-ice pass from Marchand but Bill Peters challenged the play as offside. After review, the ref agreed and overturned the call.
The Flames started the second period on the powerplay and 44 seconds in it became a two-man advantage but they weren't able to capitalize.
Shortly after, the Bruins finally got on the board when Bergeron turned and fired a bouncing pass from David Krejci.
Then it was time for another edition of the Backs and Fro Show, when Backlund picked up a puck and swooped towards the net, feeding Frolik as he skated backwards across the top of the crease and redirected it in at 3:32.
"Every time you score, your confidence goes a little higher," said Frolik. "After you feel more comfortable out there and that's the way it felt tonight."
Later, Frolik got a golden chance to complete the hat-trick on a breakaway but put a rising backhand over the net.
Marchand brought the visitors back within two with 6:11 left in the second, cashing in a long cross-ice pass from Bergeron.
Tkachuk's marker was the lone tally of the third period.
"Fro, that's how he practices," said Peters, when asked about his forward's bounceback game. "Fro has been outstanding in practices, his attitude has been very good. Everyone wants to play more, everyone wants more opportunity and you saw what he did with his opportunity when he got back in the lineup. He took advantage of it. Really good, and I know the guys were really happy for him."