Stamkos chased down a loose puck and scored into an empty net with 13 seconds left to tie Pittsburgh's Sidney Crosby for the league lead. Crosby scored twice in the Penguins' win over the New York Islanders. Washington's Alex Ovechkin remained at 50 after he was held scoreless earlier Sunday in the Capitals' loss to Boston.
Mike Smith made 30 saves for the Lightning, who finished the season with three straight wins.
Rostislav Olesz scored for Florida and Scott Clemmensen stopped 28 shots.
Olesz scored at 2:06 of the first give the Panthers a 1-0 lead. He dug the puck out of the corner, then brought it out and shot from the right circle. The puck trickled under Smith's pad for Olesz's first goal in 32 games.
The Lightning tied it on Tanguay's goal at 8:01 of the first. Brandon Bochenski took a shot from the slot. Clemmensen stopped it but Tanguay swooped in for the rebound and put it in with a wrist shot.
The Lightning took a 2-1 lead a few minutes later when Lecavalier put a wrist shot high into the net over Clemmensen at 10:20.
Stamkos had several other chances to score. Clemmensen made a pad save after it appeared Stamkos had him beat with a deke to the backhand at 14:23 of the first.
At 20 years, 2 months and 3 days, Stamkos is the third-youngest player to reach 50 goals in a season. Only Wayne Gretzky (19 years, 2 months) and Jimmy Carson (19 years, 8 months) were younger when they had a 50-goal season. Stamkos, the No. overall pick in the 2008 NHL draft, is the 88th player to reach the mark.
Vincent Lecavalier has the single-season franchise mark for Tampa Bay with 52 goals set during the 2006-07 season.
The Lightning missed the playoffs for the third straight season but finished with their highest point total (80) since recording 93 in 2006-07.
Florida hasn't made the playoffs since the 1999-00 season.
NOTES: Tampa Bay recalled defenseman Scott Jackson from the Norfolk Admirals of the AHL. Jackson made his NHL debut in Sunday's game...The Panthers are 7-5-2 with two ties in season finales in franchise history, while the Lightning improved to 3-12-1 with one tie in season-ending games.