Pettersson gave Vancouver a 4-3 lead at 1:16 of the third period, swiping in a bouncing puck after Schenn's soft shot toward the net was knocked down by Carson Soucy.
Garland shot into an empty net at 18:35 to push it to 5-3.
"I mean, it's nice to get it out of the way," Pettersson said. "I mean obviously, it took way longer than we hoped for, but it is what it is. We're happy about today, and we just got to reset for tomorrow."
Schwartz cut it to 5-4 with a power-play goal with 30 seconds remaining.
The Kraken then had another chance to tie it, but Andre Burakovsky's last-second shot was blocked by J.T. Miller, who injured his left ankle on the play and needed to be helped off the ice after the buzzer sounded.
"Just to hear that music in the room and know how hard they've practiced," Boudreau said. "They've never given up hope. I know it's only one game, but I mean, the spirit has never been down where we've gone into a game and go, 'Oh, woe is me.' So, I think it was a great reward for them."
NOTES:Boudreau became the second-fastest coach in NHL history to win 600 games (1,049 games), behind Scotty Bowman (1,002). … Mikheyev's goals were his first with the Canucks since signing a four-year contract this offseason. … Eberle's first assist on Beniers' goal was his 600th NHL point. He has 262 goals and 339 assists in 867 games.