WATCH: [All Penguins vs. Panthers highlights]
It was the first NHL hat trick for Dadonov, who played 55 games for the Panthers from 2009-12 before spending five seasons in the Kontinental Hockey League.
"He's an elite goal-scorer in this league and in this world," said Florida center Aleksander Barkov, who had three assists, all on Dadonov's goals. "He was scoring a lot of goals in Russia and it was just a matter of time when the puck started going in. He's been a dangerous player the whole year and now he just had those good chances, he put them in."
Vincent Trocheck, Jamie McGinn and Derek MacKenzie scored for the Panthers, who have won nine of their past 12 (9-3-0) games. Roberto Luongo made 32 saves.
The Panthers (28-25-6) remained five points behind the Columbus Blue Jackets for the second wild card into the Stanley Cup Playoffs from the Eastern Conference with three games in hand.
"We're confident in what we have in this locker room," Luongo said. "We've had some success lately and that builds a little more confidence in our group and the way we play. We feel that when we're playing well, we can beat anybody."
Evgeni Malkin had two goals and an assist for the Penguins, giving him 38 points (22 goals, 16 assists) in his past 21 games. Carl Hagelin and Bryan Rust each had a goal and an assist, and Patric Hornqvist scored.