Jeff Halpern tied it at 1 in the second period with his eighth goal, and Plekanec put Montreal up 2-1 with his 17th at 5:46 of the third. Gionta, who scored twice in Tuesday's shootout win at Washington, made it a two-goal lead at 11:32 with his 19th.
Auld, who blew a 4-0 lead in his last start, improved to 4-2 in eight games. The Canadiens, who won in a shootout in Washington on Tuesday night, improved to 9-2-3 in their last 14 games.
Stephen Weiss scored with 2:10 left to draw Florida within one. Scott Timmins netted his first NHL goal for the Panthers, who lost their third in a row. Tomas Vokoun stopped 38 shots.
Florida has only one win in eight games (1-3-4).
Auld earned his first win in two starts in Montreal, including a no-decision on Jan. 17 when he allowed four goals before being replaced by Carey Price in the Canadiens' 5-4 shootout win over Calgary.
Halpern made it 1-1 at 4:50 of the second when he deflected P.K. Subban's point shot past Vokoun.
Plekanec, who assisted on one of Gionta's two goals in Washington on Tuesday, gave the Canadiens their first lead when his shot into traffic flipped into the air and found its way into the net.
Gionta scored his third goal in two nights when he beat Vokoun from the right side to give the Canadiens a 3-1 lead.
Weiss made it a tight finish when he jumped on a rebound and fired the puck into an open right side with 2:10 remaining.
Timmins gave Florida a 1-0 lead 7:30 into the game, scoring for the first time in two games after being called up from Rochester of the AHL on Tuesday. He made his debut in the Panthers' shootout loss at Toronto on Tuesday.
NOTES: Timmins was chosen 165th overall by the Panthers in the sixth round of the 2009 draft, which was held in Montreal. ... Auld was 7-13-5 with one shutout and a 3.34 goals-against average in 27 games with Florida in the 2006-07 season.