Germany's Maria Riesch and Finland's Tanja Poutiainen repeated their silver-bronze placings at the first slalom of the season in Levi, Finland.
Pietilä Holmner, who won world championship silver in the giant slalom at Are in 2007, claimed the first World Cup victory of her career. She led after the first run and was fastest also on the second as she finished 0.68 of a second in front of Riesch and 0.93 in front of Poutiainen.
"My first win! I can't describe it," the elated 24-year-old said. "It brings me to tears. I feel super good."
Riesch, the Olympic and world champion in the discipline, was seventh after the first run, but delivered the second-fastest second-leg performance to reach the second step of the podium.
She also regained the lead in the overall World Cup rankings, a day after she had been supplanted by compatriot Viktoria Rebensburg thanks to Rebensburg's runner-up finish in Saturday's giant slalom.
"I can be happy with this race," Riesch said.
Austrian Marlies Schild, who won in Levi, failed to qualify for the second run here after she straddled the first gate on the course in the opening leg.
"Short day," said Schild, who earned slalom silver at the Olympics">Vancouver Olympics and bronze at Torino four years earlier. "This doesn't happen. Never."
With her eighth-place finish, American Lindsey Vonn of nearby Vail claimed some valuable World Cup points. She notched the fifth-fastest time on the second leg as she bounced back from her disappointing giant slalom performance on Saturday, when she skied off the course on the first leg.
"It's the hill that never quits," Vonn said of a course where she has often struggled. "This hill is just tough and you try to do the best that you can."
Czech slalom specialist Šárka Záhrobská, who had won the event here the past two years, settled for 12th place.