Nicolas Roy kept the puck during a 2-on-1 rush and scored to get the Golden Knights within 2-1 at 14:20 of the second. It was Roy's fifth point (two goals, three assists) in his past six games.
"They transitioned the puck extremely well," Wagner said. "Every time they get the chance, they're going quick up, and as a team we know we have to get better at that against them on Wednesday. We had a tie game going into the third, and it just happened that way."
Wagner scored on a breakaway at 9:41 of the first period to give the Kings a 1-0 lead.
Kopitar made it 2-0 at 8:57 of the second on a one-timer set up by Dustin Brown's pass from behind the net.
Alex Iafallo had the secondary assist on Kopitar's goal. The 27-year-old forward signed a four-year, $16 million contract (average annual value of $4 million) on Monday.
Pacioretty scored 226 goals in 10 seasons with the Montreal Canadiens and has 74 in three seasons with the Golden Knights. He is the 25th active NHL player with 300 goals.
"I've said this numerous times, it's the best shot I've ever played with," Stone said. "Probably the best goal-scorer I'm ever gonna play with. I don't know if there's five guys in the League that shoot it harder than him, and he has precision. You see it on that goal."
NOTES: Defenseman Dylan Coghlan played as a wing on the fourth line for the Golden Knights, who did not have forwards Ryan Reaves and Keegan Kolesar available after each sustained an undisclosed injury against the Coyotes on Sunday. … Brendan Lemieux had an assist on Wagner's goal. It was Lemieux's first point in three games for the Kings since he was acquired in a trade from the New York Rangers on March 27. … Brown (one goal, three assists), Iaffalo (two goals, one assist) and Kopitar (one goal, two assists) each has a three-game point streak.