Ivan Barbashev and Paul Cotter also scored, and Eichel had two assists for Vegas. Logan Thompson made 26 saves.
Noah Cates and Cam Atkinson scored, and Hart made 26 saves for Philadelphia (3-2-1).
“We played 40 really good [minutes]. You don’t want to be on your heels. We talk about it in between periods,” Flyers coach John Tortorella said. “They turned it up. They threw caution to the wind. You end up backing up a little bit and being tentative. Some of our younger players felt it a little bit. These are the lessons we’re going to have to go through.”
Barbashev gave the Golden Knights a 1-0 lead at 6:54 of the first period, scoring five-hole on a rebound in front.
“He was more involved. I liked his game,” Vegas coach Bruce Cassidy said. “He was working to his spots. He was better on the walls. Good for ‘Barbie.’ He’s a good hockey player. His game is going to get in order.”
Cates tied it 1-1 at 13:07. He knocked in a rebound near the right post after Joel Farabee batted his saucer pass on net.
Atkinson gave the Flyers a 2-1 lead at 17:19 of the first when his backhand from a bad angle hit off the blocker of Thompson, deflected down onto his left pad and bounced into the net.