American Lindsey Vonn won her second slalom of the World Cup season on Friday, thwarting best friend Maria Riesch's attempt to collect her fifth successive victory in the discipline.

"I would have loved to share this victory with Maria but we'll try to be joint world champions in Val d'Isere," said Vonn after beating German Riesch into second place by 0.90 seconds.

Vonn, the overall World Cup holder and current leader, skied an authoritative second leg to win in a combined time of one minute 47.17 seconds.

Austrians Kathrin Zettel and Michaela Kirchgasser, who had been ahead of Vonn after the morning leg, both made big mistakes in the second run. Zettel was disqualified while Kirchgasser failed to finish.

"I was in two minds before the second leg between taking risks to win or ski a safe run to score points," Vonn told reporters.

"I did not race to the full limit and I'm very surprised to win this especially as the Austrians had a comfortable lead.

"I expected to win more than one downhill this season and certainly not two slaloms," added Vonn, who won her maiden slalom victory in November in the Finnish resort of Levi.

Riesch said being pre-race favourite had put her under pressure.

"I was under enormous pressure to try to win my fifth slalom in front of my home crowd. I only managed to calm down in the very end of the second run when I skied well at last. It was a little bit too late," said the German, whose younger sister Susanne clocked the fastest time of the second leg.

Unheralded Slovenian Marusa Ferk finished third, 1.18 behind Vonn, for her first podium placing in a World Cup race.

It was Vonn's fourth victory this season, after Levi, a downhill in Lake Louise and a super-combined in Altenmarkt. With 17 World Cup wins, she is only one short of the American record of Tamara McKinney in the 1980s.

With 1,014 points, Vonn strengthened her World Cup lead ahead of Riesch, who is on 890.

Anja Paerson of Sweden, who is joint third in the overall standings, missed a gate in the first run.

Men and women are both in action in Garmisch on Saturday, the men competing in a downhill while the women have a super-G, their last race before the world championships start in Val d'Isere, France, on Tuesday.