Vonn's first run in the giant slalom, which is not her strongest discipline, was not quick enough to ensure a second descent as Germany's Viktoria Rebensburg won from Tessa Worley of France and Italy's Manuela Moelgg, with American Mikaela Shiffrin fifth.
The 33-year-old Vonn missed much of last season after breaking her arm in a training crash in November that led to nerve damage in her right hand which required surgery and extensive rehabilitation.
"Not the result I was looking for today but still a positive experience. 1st GS race in over 600 days. Now looking to Lake Louise! Progress!" Vonn tweeted afterwards.
She added: "When I am able to do what I love and I'm healthy, I have to smile!"
Vonn is striving to make history this season as she chases Ingemar Stenmark's all-time record of 86 World Cup wins. She already holds the women's record and is just nine wins adrift of the Swedish great.
The speed specialist's first realistic chance to close the gap will come in a series of downhills and super-G races at Lake Louise -- dubbed "Lake Lindsey" because of her dominance at the Canadian resort -- from November 28.
Vonn won the Olympic downhill title in 2010 but missed out defending in 2014 after a series of knee injuries.
Rebensburg, the 2010 Olympic giant slalom champion, overcame a 0.33-second deficit on Moelgg after the first run to triumph on the Rettenbach glacier for her 14th World Cup victory. Her first also came in a giant slalom at Soelden in 2010.
Worley, the reigning World Cup giant slalom champion, finished 0.14 secs adrift, while Moelgg let slip her first-run lead to come 0.53 secs behind.
Shiffrin, 22, missed out on a fourth successive Soelden podium following victory in 2014 and second the next two years.
The Olympic slalom champion was second after the first run but finished 0.74 secs behind.
The men's opening giant slalom race scheduled for Sunday in Soelden was canceled because of high winds and bad weather.
Austrian Marcel Hirscher, who has won the World Cup giant slalom title for the last three years, was already going to miss the start of the season after breaking his ankle during pre-season training.
But American Ted Ligety, the five-time World Cup giant slalom champion, was set to make a comeback after ending his 2016/2017 campaign prematurely for back surgery.
The circuit moves onto Levi in Finland for men's and women's slalom races on November 11 and 12.