Matt Roy and Viktor Arvidsson also scored, and Gabriel Vilardi had three assists for the Kings (23-14-6), who had lost two of three. Pheonix Copley made 19 saves.
"We were prepared to play the right way. Vegas presents a lot of different challenges," Los Angeles coach Todd McLellan said. "We played the way we wanted to and the game plan we wanted to. That was player one through 20. Definitely a good team win."
Jonathan Marchessault scored in his return after missing six games with a lower-body injury for the Golden Knights (27-13-2), who had won three straight. Logan Thompson allowed three goals on 19 shots before being replaced at the start of the third period by Adin Hill, who made two saves.
"It was probably the most disappointing game of the year for us when I look at our competitiveness from top to bottom," Vegas coach Bruce Cassidy said. "Obviously, I'll look at myself to see what I do to prepare the players. I thought our first little bit was good, but once we got behind, I don't think we had the bite in us to get back in the game. The will. The compete. Whatever adjective you want to use. And you should."
Fiala gave the Kings a 1-0 lead at 17:02 of the first period, turning around above the high slot and scoring through a screen.
"I kind of turned. I wanted to give it to a defenseman, but I saw nobody come at me, and looking at the goal, there was a lot of traffic there. So I just threw it on net and see what happens," Fiala said. "I had a good lane. It was open. I was hoping nobody would get there."
Prior to the goal, the Golden Knights had a few opportunities to take the lead, but William Karlsson hit the post at 2:56, and Marchessault hit the crossbar at 13:37.
"There wasn't much good, but the good was we created three good looks," Cassidy said. "Maybe it's a different game if those go in."
Roy made it 2-0 at 9:27 of the second period with a short-handed goal. He scored after Thompson knocked away Rasmus Kupari's soft shot to him in the right circle.
"That's big. [Roy] works hard, and to see him get rewarded, that's awesome," Copley said. "They're tough to score on on the power play, so when the PK comes through like that, it's obviously big."
