Brayden Point extended the lead to 3-0 at 14:36 of the third period when he made a cut around Panthers defenseman MacKenzie Weegar and tucked the puck past Knight's outstretched left pad.
"Obviously disappointed. I thought we had our chances in this series, could have went either way," Panthers forward Jonathan Huberdeau said. "Early we're down 2-0, could have went the other way. It's going to take a little bit to swallow this one, but that's the most fun I had this year. We had a good group, it just didn't go our way in the first round."
Alex Killorn shot into an empty net at 18:18 for the 4-0 final.
"You've probably heard the fourth one is the toughest to win in a series, and when you have a chance to do it you don't want to waste them," Tampa Bay coach Jon Cooper said. "We had a plan set. But the players … it was 60 minutes of sheer will and compete. And to win in this league that's what you need. When you make the playoffs, you need it from everybody. The players gave it. They get all the credit in the world."
NOTES: Lightning forward Barclay Goodrow (upper body) made his series debut and had three shots and five hits in 16:43 of ice time. … Kucherov led the series with 11 points (three goals, eight assists). … Vasilevskiy's shutout was his second in the Stanley Cup Playoffs. His other was against the Dallas Stars in Game 6 of the 2020 Stanley Cup Final, when Tampa Bay won its second championship.