Florida, which won the Presidents' Trophy for having the best record in the NHL during the regular season, was eliminated with the loss.
Thornton was a healthy scratch in the Panthers' first nine playoff games. The 42-year-old forward was minus-1 in 6:18.
"I think he'll bring energy, enthusiasm and it rubs off on our guys, and I think we need that," Florida coach Andrew Brunette said before the game. "I think they're a little bit down the last couple games, especially after that Game 2 (a 2-1 loss), and we need a little bit more energy and more life out of our group here tonight."
RELATED: [Complete Panthers vs. Lightning series coverage]
Thornton, who signed a one-year contract with the Panthers as an unrestricted free agent Aug. 13, 2021, had 10 points (five goals, five assists) in 34 regular-season games with the Panthers. He leads active NHL players with 1,539 points (430 goals, 1,109 assists) in 1,714 regular-season games over 24 seasons with the Boston Bruins, San Jose Sharks, Toronto Maple Leafs and Panthers.
Thornton is also fifth among active players with 134 points (32 goals, 132 assists) in 186 NHL playoff games.
"I don't think I can say anything that hasn't been said already about a future Hall of Famer," Lightning coach Jon Cooper said. "I was fortunate enough to meet him at the 2019 San Jose All-Star Game, so I got to spend some time him. What a class individual. They're down in the series, so they're changing things up, and I think there's a lot worse guys in the League to put in than Joe Thornton. … He's just a class, great guy."
Forward Anton Lundell also played for Florida after being a healthy scratch in a 5-1 loss in Game 3 on Sunday; he had one shot on goal in 11:50.
Forwards Anthony Duclair, who has one goal in eight playoff games after scoring 31 during the regular season, and Ryan Lomberg came out of the lineup.
