Kim Clijsters overcame Croatia's Karolina Sprem 6-3, 6-2 to reach the quarter-finals of the Filderstadt Grand Prix in Filderstadt, on Thursday and edge closer to the number one spot.
The second-seeded Belgian, who could replace Maria Sharapova at the top of the rankings this week, always looked in control against the qualifier.
But the match was far more competitive than the score suggested. Sprem, who enjoyed a promising 2003 season but then faded, is clearly getting back to the form that allowed her to beat Venus Williams at Wimbledon last year.
She returned well and often had Clijsters struggling to stay in the rallies but was ultimately let down by her lack of consistency.
"It was quite a battle," said Clijsters. "I've played her before and today she was a lot more steady. She's got a lot of power and really goes for her shots and when it goes in it's very tough and you have to defend well.
"But I knew that once I could break her rhythm a little bit and keep getting enough balls back that eventually she would miss, and she did. I felt good and did what I had to win, and that's important in these kind of matches."
The Belgian needed six break points to establish a 2-0 lead, but Sprem immediately broke back. Clijsters then needed another six break points before breaking again for 4-2.
The pair exchanged breaks at the opening of the second set, before Clijsters won four games in a row to build a 5-1 lead. Clijsters then held one match point on Sprem's serve before serving out for the match.
Clijsters will next face fifth seed Elena Dementieva, who emerged from an absorbing battle against Nathalie Dechy of France with a 5-7, 6-3, 6-4 victory.
STRICKEN OPPONENTS
Amelie Mauresmo and Nadia Petrova earned easy victories over flu-stricken opponents to reach the quarter-finals.
Sixth-seeded Petrova won 6-1, 6-1 against fellow Russian Elena Likhovtseva and third seed Mauresmo of France was 6-0 up when her Serbian opponent Jelena Jankovic retired after losing the first three points of the second set.
Likhovtseva, who had previously won three of her five meetings with Petrova, had an early opportunity to take the lead but failed to convert two break points at 1-0. From then on Petrova was never troubled.
She broke to lead 2-1 when Likhovtseva made a backhand error and after a fine forehand volley gave Petrova a second break for 4-1 Likhovtseva summoned the trainer and a doctor.
After having her blood pressure checked and leaving the court for a short time to be evaluated further, Likhovtseva continued but made little impact and Petrova closed out the 55-minute match with an ace.
Jankovic, who also called for the doctor after dropping the first set, looked pale but did occasionally produce a competitive rally.
Mauresmo, though, was in superb form, sometimes serve-volleying and constantly causing damage with her trademark backhand.