Gagnon finished sixth with a combined time over two runs in the World Cup slalom of one minute, 46.81 seconds. The Lac-Etchemin, Que., native, who was eighth after the first run, finished 1.64 seconds back of the winning time.
Gagnon briefly held the lead after the second run, but several of the first run leaders had yet to complete their day.
MarliesSchild of Austria had a brilliant final run to move from third to first, flipping the order on the podium with younger sister Bernadette, who led after the first. Marlies Schild clocked 1:45.17, finishing 0.33 seconds ahead of FridaHansdotter of Sweden.
It was the winner's 34th career World Cup slalom win, but first since February 2012.
Tessa Worley injured
Brittany Phelan of of Mont-Tremblant, Que., also finished in the points, coming in 27th. Erin Mielzynski of Guelph, Ont., continued her struggles so far early this season, not making it to the second run.
American Mikaela Shiffrin, last year's discipline champion, finished 12th. Tina Maze, overall champ from 2012-13, finished 17th.
Former overall champion Maria Hoefl-Riesch started strongly before going off course in the first run, while Tessa Worley - a Frenchwoman who won a giant slalom in St. Moritz on Sunday - went back on her skis and appeared to injure her right knee.
Worley toppled backward before twisting forward and landing in the safety netting.
She lay still for a few moments before getting slowly back up. She was taken down the slope on a stretcher and to a hospital in Lyon, where she was to undergo tests. No further information was immediately available.