Thompson, last year's world silver medallist, delighted her home crowd by edging Switzerland's Fanny Smith and France's Ophelie David, the six-time world champion, into the minor medal placings.
Devouassoux took gold ahead of Switzerland's Armin Niederer and Canada's Brady Leman in sub-zero conditions that had delayed the event by 24 hours.
Meanwhile, British Olympic hopeful Emily Sarsfield opened her season with a solid 24th place.
Sarsfield missed the 2010 Games in Vancouver after tearing knee ligaments and fracturing a femur and tibia in a crash and needs to be ranked inside the world's top 32 in January to be considered for selection.
She later blamed a minor mistake at the bottom of the course for costing her a place in the quarter-finals.
British team-mate Pam Thorburn ranked 35th.