The 27-year-old American is now just four short of the women's record of 82 World Cup victories set by Lindsey Vonn, who retired in 2019, and is also on track for the 86 World Cup victories of Swedish great Ingemar Stenmark.
The overall World Cup leader took a grip on the event with a dominant performance in the first run when she finished 0.72 seconds ahead of Slovakian Petra Vlhova with French skier Tessa Worley just 0.01sec further back.
Going last in the second run, Shiffrin was more cautious, clocking the sixth best run, but it was still enough to ensure her fourth World Cup win of the season, 0.13sec ahead of Vlhova.
"The start of a weekend with three races is always a bit nerve-racking," said Shiffrin.
"You hope that you’re in the right shape and you can bring the right intensity from the start.
"I felt very good today, the second run was difficult to master, but it's a pleasure to ski here."
Italian skier Marta Bassino, who was fourth after the first run, pipped Worley to complete the podium and maintain her position at the top of the discipline standings. Olympic champion Sara Hector finished down in eighth.
Shiffrin, who also won two slaloms at Levi and the Super-G at St. Moritz, now has 675 points in the overall standings, 205 ahead of the Italian speed specialist Sofia Goggia who is not competing in Semmering.
The American is fifth in the discipline standings, 80 points behind Bassino.
She will have a chance to close the gap further when the women take on a second giant slalom on the Semmering slopes on Wednesday with a slalom to follow on Thursday.
