While Miller's form has improved in recent weeks, he took a step backward Sunday when he finished 35th in a race won with a perfect run from Svindal.
"This wasn't good for my confidence," Miller said. "But my skiing was fine."
Miller was an early starter and attributed his troubles to snowfall during the first half of his run.
"I couldn't see anything," the two-time overall winner said. "Not seeing makes the bumps much worse. But I've been skiing well. I skied well in the training runs, so we just got to stay focused."
Svindal mastered the fresh snow conditions on the Stelvio course for his fourth victory of the Olympic season, with just 40 days to go to the Sochi Games.
The Norwegian clocked 1 minute, 54.08 seconds to finish 0.39 seconds ahead of Hannes Reichelt of Austria.
Erik Guay of Canada placed third, 0.51 back, for a strong follow-up to his downhill victory in Val Gardena a week ago.
Svindal trailed Guay at every checkpoint but then gained 0.65 seconds over the last few gates, where Guay made a slight but costly error, lifting up his left ski to regain his balance after cutting off a turn too sharply.
The Stelvio is known for its knee-jarring bumps, making fatigue a big factor.
"You win Bormio in the last part, because everyone is tired. It's a mix of you're tired and it's a bit scary," Svindal said. "
Svindal has finished in the top five in his last six World Cup downhill races and in 12 of his last 14 dating back to March 2012.
With Miller struggling, the top American finisher was Travis Ganong of Squaw Valley, Calif., in 11th place.
In Lienz, Austria, overcoming several injury-plagued seasons, Marlies Schild of Austria finally set the record for most World Cup slalom victories by winning her 35th race to overtake Switzerland's Vreni Schneider on top of the all-time list.
The 32-year-old Schild is a four-time World Cup slalom champion, but she missed a host of races after breaking a leg in 2008 and then tore ligaments last year. That meant she was stuck on 33 slalom wins for close to two years until winning in Courchevel, France, this month.
Schild got her record-setting win in impressive style. Lying 0.69 seconds behind in sixth after the opening leg, she used a blistering second run to finish in 1 minute, 55.63 seconds and beat American teenager Mikaela Shiffrin, who led the competition after the first run. Shiffrin finished 0.41 behind.
Olympic slalom champion Maria Hoefl-Riesch of Germany was third, 0.63 behind Schild.