Mike Hoffman and Evgenii Dadonov scored for the Panthers (32-24-6), who are 3-7-1 in their past 11 games and remained two points behind the Toronto Maple Leafs for third place in the Atlantic Division. Sam Montembeault made 34 saves.
"We had some stretches in the game where I thought we had some good momentum," Florida coach Joel Quenneville said. "I think we give up goals too easy, I'd say. That's the frustrating part."
Hoffman scored on a rebound at 3:28 of the first period to give Florida a 1-0 lead.
Tomas Nosek tied it 1-1 at 11:52 with a wrist shot from the slot.
Dadonov scored his 25th goal of the season, on the power play 42 seconds into the second period, to give Florida a 2-1 lead. He one-timed a cross-ice feed from Aleksander Barkov in the right circle for his 200th NHL point.
Carrier tied it 2-2 with a wrist shot from the left circle at 12:39, and Pacioretty finished a 2-on-0 with Shea Theodore at 19:08 to give the Golden Knights a 3-2 lead.
Smith scored 19 seconds into the third period to make it 4-2.
"We started fine, but once the game kept going, they got the momentum," Barkov said. "They outskated us, they outchanced us, put pucks on the net. You need a full 60-minute effort."
Aleksi Saarela made it 4-3 after an unsuccessful challenge for goalie interference at 5:11 of the third, but Smith scored an empty-net goal with 1:17 remaining for the 5-3 final. It was his 25th goal of the season.
"He's such a valuable guy," Golden Knights coach Peter DeBoer said of Smith. "You use him in every situation; he's so good defensively, and he's scored some timely goals. I've only been here for a dozen games or so, but he's scored some big goals and some timely goals for us. That was a huge one tonight; they were pressing. That goal early in the third, I thought, was probably the difference in the game."
