MEMPHIS, TN, USA - Sabine Lisicki showed another example that she is returning to the form that saw her reach No.12 in the world last year in fending off the challenge of rising American star Madison Keys on Tuesday at the US National Indoor Tennis Championships.

Though the 18-year old Keys climbed to a career-high No.79 this week, Lisicki is on her own hot streak. The World No.40 was a runner-up at her last WTA event in Pattaya City and followed that up with a win for Germany in Fed Cup action. And now with 75 63 defeat of Keys in her opener here, in which she rallied from a 5-3 first set deficit, she has been victorious in six of her last seven matches.

"I didn't serve too well in the beginning," the third-seeded Lisicki said. "But I executed at the right moments and broke her when she was serving for the first set, and everything went well from there on. I had never seen her play, so I had to get used to her style, and once I did that, things went well."

There was a first round upset, with qualifier Claire Feuerstein a 63 64 victor over No.5 seed Lucie Hradecka for just her second WTA main draw match win. The Frenchwoman had been 0-3 in her series with Hradecka without having won a set.

Second round play also got underway, with seventh-seeded Magdalena Rybarikova and Jamie Hampton securing quarterfinal spots. The 2011 Memphis champion, Rybarikova was a 76(2) 62 winner over Lauren Davis, and Hampton handled fellow American Coco Vandeweghe, 63 60, reeling off 11 straight games after starting the match in a 3-1 hole.

"It started off a little rough," Hampton said. "I never played Coco before, but I know she can play some big tennis and is very talented. So I was very cautious today, but I played my game and in the end it worked out for me."

No.1 seed Sofia Arvidsson, No.2 seed Kirsten Flipkens and Lisicki are among those on Wednesday's schedule. Arvidsson, a two-time champ here, takes on her victim in last year's final - Marina Erakovic.