"That's really exciting, for sure".
"It's an incredible moment right now", said Shiffrin.
Holdener needed a top two finish to have any hope of keeping the title race alive.
Attention will now turn to a slalom race tomorrow. Vonn has four overall titles, winning in 2008-10 and 2012. The finish was enough to secure Shiffrin's second straight overall World Cup title. Lindsey Vonn, who did not race this weekend but will be in Are, holds the record of 81 wins.
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Merkel, aged 63 and in power for 12 years, is due to formally launch her fourth-term government next Wednesday. The overall balance is tipped by Merkel's Bavarian allies, who nominated three men.
Shiffrin had not raced since the Olympics. She also won a gold in the GS to go with her gold in slalom from the 2014 Sochi Winter Olympics. She leads Switzerland's Wendy Holdener by more than 500 points in the overall standings. "The best thing for me now is to have the crystal globe already locked in".
But the largest globe is now hers heading in Are.
Giant slalom standings leader Viktoria Rebensburg of Germany was second, 0.66 seconds behind, just missing the victory that would have guaranteed her the title in the event.
Shiffrin now carries a 603-point lead into next week's World Cup Finals in Are, Sweden, and mathematically clinches her second-straight overall World Cup title.
United States' Mikaela Shiffrin poses on the podium after placing third in Friday's World Cup giant slalom in Ofterschwang, Germany.