Demko made two tough in-tight saves on Viktor Arvidsson before Conor Garland made it 2-0 at 5:43. Vasily Podkolzin's shot went wide, pulling Petersen out of position, and Garland tucked the puck inside the right post.
"They were playing for first impression and they played well," McLellan said. "But we have to answer the bell better than we did."
Elias Pettersson, who had an assist, shot wide on a penalty shot at 16:43, but Juho Lammikko, who was a healthy scratch the previous five games, scored his first goal of the season following a turnover by Rasmus Kupari at 6:59 of the third period to make it 3-0.
"The backbreaker was obviously the third goal, which is preventable," McLellan said. "Anything can happen in the NHL, but at that point, the way they were playing and the way we were playing, it was the nail in the coffin."
Miller made it 4-0 with a one-timer off a pass from Boeser on the power play at 12:48.
"[Boudreau] gave me [heck] for that one," Boeser said of passing instead of shooting.
Defenseman Alexander Edler was playing his first game against Vancouver since signing with Los Angeles as a free agent on July 28. He spent his first 15 seasons with the Canucks and received a standing ovation when he was honored on the scoreboard in the first period.
"This is a great building to play in, a great city to play in and the fans are great, so that was a special moment for me and I'm always forever thankful for what this city has done for me," Edler said.
NOTES: Canucks defenseman Travis Hamonic had two shots, two hits and three blocked shots in 17:35 of ice time after being recalled from Abbotsford of the American Hockey League earlier Monday. … Pettersson has scored 13 points (five goals, eight assists) in eight games against the Kings, Boeser has scored 13 points (eight goals, five assists) in 11 games, and Miller has scored 15 points (five goals, 10 assists) in 14 games. … Vancouver is 6-0-0 when Miller has a multipoint game this season.