Filderstadt, Germany Martina Hingis, seeking to protect her No. 1 ranking, struggled to a 0-6, 6-4, 6-2 victory over Magdalena Maleeva at the Porsche Grand Prix on Wednesday.
Hingis has gone through 12 tournaments since February without winning a title, the longest drought of her career.
The Swiss standout could lose her No. 1 ranking this week to Jennifer Capriati of the United States.
Capriati, the Australian and French Open champion, stayed on pace by easing past qualifier Miriam Oremans of the Netherlands 6-1, 6-4 to join Hingis in the quarterfinals. Both had first-round byes.
Hingis won her first professional title in Filderstadt in 1996 and has won the event four of the last five years, including the last two.
Anne Kremer, a qualifier form Luxembourg, rallied to beat an erratic Anna Kournikova 4-6, 6-2, 7-5 in a first-round match, dealing the 20-year-old Russian another setback in her slow comeback from injury.