The 20-year-old was the woman to beat as the World Cup circuit arrived in France for the third event of the season having won the opening two rounds in Nakiska and Telluride.
And she proved exactly why by winning the big final, although she was given a helping hand after Andrea Limbacher and Marion Josserand both fell not long after coming out of the start gates.
The Swiss skier did trail Marte Hoeie Gjefsen following the Norwegian fine start however she made her move just over a half way down the run for her third win of the season.
Limbacher recovered to take third ahead of Josserand with Smith extending her lead in the ski-cross World Cup standings to 118 over Ophelie David, who failed to make the semi-finals in Val Thorens.
Meanwhile Smith's Swiss team-mate Armin Niederer took his second win of the season in a far less dramatic race to extend his overall ski-cross World Cup lead from 40 to 60 points.
Niederer, third last time out after winning the season opener in Nakiska, held off Brady Leman to come out on top with fellow Canadian David Duncan edged out of third by Joe Swensson.
However second was good enough for Leman to take second outright in the World Cup standings, having been level with Alex Fiva after round two, the Swiss skier not reaching the semi-finals.