Dadonov, who also had an assist, had his first multipoint game with the Golden Knights. The forward was acquired in a trade with the Ottawa Senators on July 28.
"I think [Dadonov's] been getting better and better. Like all goal scorers he's a streaky guy," Golden Knights coach Peter DeBoer said. "When I look back at the first dozen games, he could easily have three or four more. If or when we get healthy … I think he's going to score consistently all year."
Marchessault scored his 100th and 101st goals with the Golden Knights in the third period and extended his point streak to six games (seven goals, two assists). He is the first player in their history to reach the milestone.
"Obviously pretty proud of that," Marchessault said. "I take a lot of pride in playing for the Golden Knights and being here since Day 1. Working hard every night, trying to help my teammates win a hockey game. VGK is the pride of my career."
Vegas forward Mark Stone had an assist in 18:38 after missing 12 games with a lower-body injury.
"Turned the puck over my first shift for a goal, took a penalty on the second shift for a goal, so it couldn't get any worse," Stone said on his start. "I definitely felt better as the game went on. I haven't even had a practice really yet. It's been a long month for me, but I'm just excited to get back out there with the guys."
Jake Leschyshyn, playing his 13th NHL game, had a goal and an assist for his first points in the NHL, and Robin Lehner made 39 saves for the Golden Knights (9-6-0), who have won eight of 10.