It was the longest active winning streak in the NHL and tied for the longest in Golden Knights history (Dec. 14, 2017 to Jan. 2, 2018).
"It's frustrating when you lose," Vegas coach Peter DeBoer said. "I think we've been on a good run lately."
WATCH: [All Kings vs. Golden Knights highlights]
The Golden Knights (36-23-8), who also had their seven-game home winning streak end, remained four points ahead of the Edmonton Oilers for first place in the Pacific Division. Marc-Andre Fleury made 13 saves.
"You look at the standings, everyone seems to be winning along with us," Vegas defenseman Nate Schmidt said. "It's hard to drop a game like that, but we've been playing really well the last couple of weeks."
Petersen made 19 saves in the third period for the Kings (25-35-6), who have won three in a row. Anze Kopitar scored two goals.
"It was a good win," Petersen said. "Obviously they were kind of hot, so we wanted to come in here, especially on the road, and have a good performance. I think everybody did their job. I made the saves I needed to make, and it worked out."
Each of Kopitar's goals were scored in the first period. He gave the Kings a 1-0 lead at 2:01 and made it 2-0 on a power-play at 7:39.