French Open winner Li Na of China was the first quarter-final casualty of Stuttgart's WTA clay-court tournament on Friday following her three-sets defeat to Agnieszka Radwanska.
Li, the 2011 winner at Roland Garros, was beaten 3-6, 6-2, 6-3 by Polish fourth-seed Radwanska, who will play either world number one Victoria Azarenka or wildcard Mona Barthel who meet later on Friday.
After dominating the first set, Li struggled to cope as Radwanska raised her game with a series of drop shots and strong returns in the second before carrying her improved form into the third.
With Roland Garros set to start on May 27, Radwanska said she is enjoying finding her feet on clay-court as she bids to win her first Grand Slam title having claimed nine wins on the WTA tour.
"I am enjoying my tennis and just trying everything at the moment," said the 23-year-old, ranked fourth in the world and who claimed her ninth tour win at Miami recently.
"I just hope this is my year, so I can take the next step."
All of Radwanska's four losses this year have come at the hands of Azarenka and having also reached the semi-finals here last year, the Polish number one said it takes a special effort to beat the world number one.
"You have to be at the top of your game and play some great tennis to beat her," admitted Radwanska.
In Friday's other last four ties, world number two Maria Sharapova takes on fifth-seed and US Open winner Samantha Stosur while Wimbledon champion Petra Kvitova faces Angelique Kerber.