Grenier, from Ottawa, held her nerve to lead both runs down the slope in Kranjska Gora to edge Italian Marta Bassino (26) by 0.37sec with Petra Vlhova (27) of Slovakia third at 0.40.

It was the first giant slalom victory by a Canadian at the World Cup since Kathy Kreiner in 1974.

"I have no words, I still can't believe it," said Grenier after also achieving her first podium finish.

"It's a dream come true, I've been wanting it for so long and I'm just going to cry because I'm so happy."

Shiffrin, chasing Vonn's record for World Cup victories, finished joint sixth overall, 1.33sec off the pace, after posting the fifth-best time in the first run and just the 18th in the second.

She will have another chance on Sunday to match Vonn's record when a second giant slalom is held in Kranjska Gora.

Shiffrin leads the overall World Cup standings but trails Bassino by 80 points in the giant slalom standings.

Fire inside

Grenier's triumph comes after she was disqualified in the first of the giant slalom races in Semmering in December for leaving the start gate too early.

"I think it almost put some fire inside of me to get my revenge, but it's revenge on myself because I messed up that day," Grenier said.

Wearing bib 12 in the first run, Grenier shocked the favourites by pushing Swiss Lara Gut-Behrami (31) into second with Italian Federica Brignone (32), the Olympic silver medallist in Beijing last year, third.

Skiing last in the second run, Grenier sealed victory with a superb lower section.

"I was a bit nervous that I would think about it too much," Grenier said.

"But I felt so good before the second run, I felt so relaxed and just excited to go."

Bassino moved up from fourth after the first run to second for her seventh consecutive giant slalom podium finish.

Vlhova's blistering second run moved her up from sixth to third for her seventh finish in the top three of the season.