Rob Blake, Sean Avery and Jeff Cowan also scored for the Kings, who have scored 21 goals while winning four of their five exhibition games.
Captain Patrick Marleau and Steve Bernier scored for the Sharks in just their second loss in seven pre-season games. MVP Joe Thornton, goal-scoring champion Jonathan Cheechoo and young regulars Milan Michalek and Matt Carle all sat out for the Sharks, who didn't provide much support for goalie Evgeni Nabokov.
Jason LaBarbera made 17 saves for Los Angeles, bolstering his bid to beat out Mathieu Garon for the Kings' backup job behind Dan Cloutier. LaBarbera, who got his first NHL shutout at the Shark Tank in Luc Robitaille's final NHL game last April, made a handful of outstanding saves in the first period, and gave up Bernier's goal on a 5-on-3 disadvantage.
The Kings didn't miss a beat without forward Eric Belanger and defenceman Tim Gleason, who were traded to Carolina earlier Friday for defenceman Oleg Tverdovsky and top prospect Jack Johnson.
Kopitar, a 19-year-old Slovenian forward, improved his case for a surprising spot on the Kings' opening-night roster.
The 11th overall pick in the 2005 draft played in Sweden last year, but looked comfortable on Frolov's line as Los Angeles took a 3-0 lead late in the first period. Frolov figured in all three goals, giving him a team-best seven points in the pre-season.
Nabokov stopped 26 shots and received a diving penalty in his last audition for the Sharks' starting job. Vesa Toskala will play San Jose's exhibition finale against Calgary on Saturday night.
Scott Thornton, a Sharks forward from 2000 until June, picked up an assist on Avery's goal. Alyn McCauley, the other former Sharks forward signed by former San Jose general manager Dean Lombardi in Los Angeles, hasn't been cleared to play after off-season knee surgery.