Coming off a 2-0 victory Wednesday night at Columbus, Johnson allowed only David Pastrnak‘s goal off a rebound at 5:55 of the third period.
Sam Bennett had a goal and an assist to help Calgary win for the third time in four games. Bennett set up winner with a backhand pass from behind the net right to Chiasson, who easily beat goalie Anton Khudobin as he scrambled to get back across.
Boston has lost three straight and four of five.
Khudobin, recalled Friday from Providence of the AHL after a brief conditioning assignment, stopped 27 shots in his first start since Oct. 22.
Khudobin needed to be sharp early as Calgary outshot Boston 13-5 in the first period and took a 1-0 lead on Bennett’s goal at 8:36.Bennett skated through a pair of Boston players outside the blue line and got in alone on Khudobin, beating him with a wrist shot.
It was the only goal of the game until Pastrnak knocked in a rebound during a scrum in front of Johnson 5:55 into the third. John-Michael Liles and Tim Schaller assisted on the goal, Boston’s first since Pastrnak scored with 11 seconds left in the first period Thursday night in a 3-1 loss at Ottawa.
The Bruins had an apparent goal disallowed 3:01 into the second after Patrice Bergeron intercepted a clearing attempt by Johnson and shot it in from the right corner. Johnson was scrambling to get up off the ice after being knocked down by Mark Giordano and the Flames challenged, getting the goal overturned after a video review showed Boston’s Brad Marchand interfered by knocking Giordano into his own goaltender.
Notes: Boston played its second straight game without D Zdeno Chara, who left Tuesday night’s loss to St. Louis early in the second period with an undisclosed lower-body injury. … The Bruins sent G Zane McIntyre to Atlanta of the ECHL. … Calgary LW Johnny Goudreau missed his sixth straight game with a broken finger. … Johnson hadn’t allowed a goal since Anthony Mantha scored for Detroit at 7:59 of the third period Sunday.
Flames: At Philadelphia on Sunday night in the fifth of six games on the road.
Bruins: Host Tampa Bay on Sunday.