J.J. Moser made it 5-1 at 6:21 of the third period, and Boyd cut it to 5-2 at 8:18 with a backdoor tap-in.
Sean Monahan scored an empty-net goal at 16:36 for the 6-2 final.
"Obviously, this is a tough place to come in to play, and really the last thing you want to do is spot them a few early into the first period," Keller said. "So I think puck management was a big part, and some of that's just, I guess, mentally not maybe being as prepared as a team as we need to be to start a game."
NOTES:Slafkovsky (18 years, 204 days) became the youngest Slovakia-born player to score his first NHL goal, passing Marian Gaborik of the Minnesota Wild (18 years, 235 days), and the fourth-youngest player to score for the Canadiens, behind Mario Tremblay (18 years, 75 days), Jesperi Kotkaniemi (18 years, 118 days) and Claude Lemieux (18 years, 141 days). Slafkovsky is also the second No. 1 pick to score his first goal in the same building he was drafted. Ed Jovanovski of the Florida Panthers was selected No. 1 in the 1994 NHL Draft and scored his first NHL goal at the Hartford Civic Center on Dec. 2, 1995.