CHARLESTON, S.C. (AP) Australian Open champion Angelique Kerber, ranked No. 2 in the world, retired because of a viral illness during her semifinal match Saturday at the Volvo Car Open, sending American Sloane Stephens to the final.

Stephens will face Elena Vesnina, the Russian qualifier who upset fifth-seeded Sara Errani of Italy 6-4, 4-6, 6-2 in the other semifinal.

Vesnina, who reached the final in Charleston five years ago before losing to Caroline Wozniacki, is first qualifier to make the finals in the 44-year history of the tournament that started on Hilton Head Island.

Stephens won the first set 6-1 and was leading 3-0 in the second when Kerber, the top seed in the tournament, retired. A trainer came to court to examine Kerber after the second game of the set. She returned to the court, but won only one point in the third game before retiring.

It's the first Charleston final for Stephens, who is making her sixth appearance in the tournament. She is also seeking her third title of the year after victories at Auckland and Acapulco.

Kerber said she wasn't feeling well while warming up but that once the match started, ''I was thinking the energy will come back and I will be feeling OK.'' But the German player found that during the first few games of the match she wasn't feeling any better.

Kerber, last year's winner in Charleston, was hoping to defend a tournament title for the first time in her career. She has won eight titles but has never repeated.

Stephens said she didn't know when the match started that Kerber was ill.

''I just thought it was going to be a battle,'' she said. ''It's understandable. It happens. I wish her well.''

Stephens said she came into this week's tournament with a different approach.

''I think I just came in thinking I have nothing to lose and I always play like garbage here. I just need to figure that out,'' she said. ''So this year I just decided I was going to come out and do the best I possibly could and if that meant I lost in the first round, then, OK, whatever.''

Vesnina, who made this year's finals by winning seven straight matches, said she has great memories of appearing in the championship five years ago.

''I knew that I could do that again. But, of course, I knew it was going to be very difficult coming from the qualifying,'' she said. It was the first time in her career she made a final as a qualifier.

It took her two hours and 20 minutes to notch the victory over Errani.

Saturday's matches were played under bright sun but in a blustery wind that from time to time sent bits of clay swirling around the edge of the court. The wind was about 25 mph with gusts up to 35.

''I'm used to playing in the wind, but the problem is today it was changing the direction - like every five minutes it was blowing different ways,'' Vesnina said. As for the finals, ''I hope it's not going to be that windy like today. Let's hope.''