The loss, Anaheim's second in a row immediately following a five-game point streak, dropped the club to 17-31-6 on the season and 8-17-5 on the road.
Lundestrom led the Ducks offensively with a two-point afternoon, including his second goal of the season. Vatrano also scored, cutting Anaheim's deficit to one heading into the third period. Trevor Zegras, Colton White and Derek Grant added assists.
Starting his third of four games since Anaheim returned from the All-Star break and coming off a franchise-record 53 saves Friday night at Honda Center, John Gibson was strong in net early to hold the Ducks in it through two periods, finishing with 32 saves.
Seven different players scored for the Golden Knights, including Paul Cotter, Shea Theodore, Phil Kessel and Jack Eichel, helping Vegas to its third straight win. Making his first start since All-Star goaltender Logan Thompson was ruled out for weeks with a lower-body injury, Adin Hill stopped 23-of-25 Anaheim shots.
Vegas wasted little time in finding the game's first lead. Just over two minutes after puck drop, the Golden Knights forced a Ducks turnover on the forecheck, capitalizing moments later when Cotter collected a rebound in the right circle and beat Gibson to the glove side.
Cotter, a 23-year-old rookie, has goals in back-to-back games and is tied for eighth among first-year NHLers in goals (10) this season.
Brett Howden doubled the lead midway through the second, finishing off a lengthy shift for the Golden Knights in the Ducks defensive zone by finding some open space in the slot and one-timing home a pass from Keegan Kolesar behind the net.
Howden has points in consecutive games for the first time this season (1-1=2).
Anaheim would respond for the end of the middle frame though, getting back within one heading to the third. Lundestrom skated the puck through the neutral zone, leaning in to protect the puck from a Vegas backchecker before directing a shot on net from in tight. Hill denied Lundestrom with the right pad, but the rebound kicked right to Vatrano on the doorstep, where he punched it home to put the Ducks on the board.