Blake Lizotte scored, and Jonathan Quick made 21 saves for the Kings (11-8-1), who are 1-2-0 on a four-game road trip that concludes Saturday at the Seattle Kraken.
"For as much as you'd like to always keep your team together and not separate it, I thought there were some individuals that let us down tonight rather than the group as a whole," Los Angeles coach Todd McLellan said. "Sometimes you have to play the game a certain way and it might not be the way you like it. It might be ugly, it might be grinding, it might not be cute, but that's the way you have to play it, and we had some that couldn't accept that or didn't want to, and that cost us."
After the Canucks allowed the first eight shots in the second period, Pettersson gave them a 1-0 lead at 5:40 with a wrist shot from just inside the top of the left face-off circle that went in between Quick's pads.
Boeser scored his first goal of the season on a power play at 10:09 to make it 2-0, redirecting a shot pass from J.T. Miller at the edge of the crease.
Lizotte cut it to 2-1 with a deflection under Demko's glove at 13:46, but Pettersson restored the two-goal lead 1:04 later after a cross-ice pass from Kuzmenko to make it 3-1 at 14:50.
"We talked lately about if we score or they score, we need to respond no matter what, not sit back," Pettersson said.
Boeser scored again at 5:07 of the third period, batting a puck out of the air behind Quick after he made the initial save against Sheldon Dries for the 4-1 final.