Benoit Pouliot scored an unassisted effort for his 17th goal 12:40 into the game. Gionta made it a two-goal lead later in the period with his 24th goal.
Halak, who made 23 saves, lost his bid for a shutout when Radek Dvorak scored 16:24 into the third to draw Florida within 2-1.
Tomas Plekanec scored his 100th goal into an empty net at 18:36 to restore the two-goal margin at 3-1. Gionta added his second of the game with Panther goalie Tomas Vokoun pulled once again to make it a three-goal lead.
Montreal blew a 2-0 lead one night earlier in Buffalo when Carey Price allowed two goals late in the third. The Canadiens went on to lose 3-2 to the Sabres in a shootout to extend their losing skid to 0-1-2 in the wake of a season-high six-game winning streak.
The Canadiens, sixth overall in the Eastern Conference with 82 points, moved within one point of fifth-place Ottawa.
Vokoun stopped 27 shots for Florida, which had won two in a row. The Panthers slipped to 12th place in the East with 71 points, one behind Tampa Bay, which won 5-3 in Boston.
Florida left wing David Booth left early in the second period after he was flattened by Jaroslav Spacek's open-ice shoulder check to the head.
A Panthers spokesman said Booth was taken to a hospital for precautionary reasons after being examined by Canadiens physician Dr. David Mulder, who said Booth was alert and coherent.
Travis Moen was wearing a visor on his helmet as he returned to Montreal's lineup after missing the Canadiens' 3-2 shootout loss in Buffalo on Wednesday night. Moen needed 50 stitches to close a horrific gash that ran from his left eyelid and up along his forehead after he was cut by Ottawa forward Matt Cullen's skate in Monday night's 2-0 loss to the Senators.
Pouliot intercepted Dvorak's attempted pass to Bryan Allen and moved to the slot, where he put a backhand past Vokoun.
Gionta drove a blast through Vokoun from the right side at 16:38 for his 24th goal to make it 2-0.
Spacek delivered his devastating check on Booth head-on 1:10 into the second and no penalty was called on the play.
Booth, who missed 45 games earlier this season after he sustained a concussion on a blindside hit by Philadelphia's Mike Richards on Oct. 24, lay face down on the ice after the hit and trainer Dave Zenobi was immediately summoned to attend to him. A bloodstain remained on the ice after Booth was helped off the ice to the dressing room.
Earlier Thursday, the executive board of the players' union voted to accept a new temporary rule that will ban hits to the head against unsuspecting players. The decision took effect immediately, starting with the 11 games Thursday night.
Notes
Booth had scored four goals in his four previous games. He has eight goals and 16 points in 28 games this season. … C Glen Metropolit and LW Mathieu Darche were healthy scratches for Montreal.