Trouba beat Akira Schmid five-hole on a backhand to help Anaheim recover from blowing a two-goal lead in the third period.
Leo Carlsson had two goals and an assist, and Petr Mrazek made 36 saves for the Ducks (10-3-1), who have won eight of nine.
Pavel Dorofeyev and Kaedan Korczak scored in the third period, and Schmid made 25 saves for the Golden Knights (7-3-4), who have lost two in a row and three of four.
Dorofeyev cut the lead to 3-2 at 3:56 of the third period to start the Vegas comeback. Jack Eichel won the draw and Dorofeyev picked up the puck, skated into the slot, and fired a wrist shot into the top left corner on the power play.
Korczak roofed a wrist shot off the left post to tie it 3-3 at 14:53.
Brett Howden gave the Golden Knights a 1-0 lead at 5:47 of the first period, one-timing a pass from William Karlsson below the goal line.
Frank Vatrano tied the game 1-1 at 15:49, redirecting an Olen Zellweger shot from the point.
Carlsson put the Ducks ahead 2-1 at 10:39 of the second period, scoring through Schmid’s five-hole.
He scored his second goal of the game at 16:50, going backhand-forehand then snapping a wrist shot underneath Schmid’s right pad.
Karlsson left the game with an undisclosed injury after the first period.
