Gionta put a wrist shot past Tomas Vokoun for his 19th goal of the season and that turned out to be the game-winner in Montreal's second straight victory.
The Canadiens scored three unanswered goals after falling behind 1-0 through one period. Jeff Halpern tied it with the only second-period goal and Tomas Plekanec put Montreal in front 5:46 into the third.
Stephen Weiss brought the Panthers back within one with 2:10 to play, but they could not come up with a tying goal against Alex Auld.
Auld made 33 saves to pick up his first win since Jan. 11.
Florida has lost seven of its last eight. Montreal has defeated the Panthers in eight of their last 11 meetings since the start of the 2008-09 season.