Maria Sharapova is on course for a third straight DFS Classic title after a 6-2 6-4 third round win over Na Li.
Sharapova still made several unforced errors
The Russian cruised into a 3-0 lead after breaking her Chinese opponent in the first and third games, only to lose the next on her own serve.
Sharapova, though, saw out the set and broke Li in the first game of the second. But Li broke again for 4-4.
But the two-time champion displayed real quality in closing out the set, and now faces Italy's Mara Santangelo.
"I was definitely better than in my first match, and I think I will keep improving. I am getting a bit of rhythm," Sharapova said.
"Conditions were a little quicker today and we had some good rallies."
Earlier, Jamea Jackson stunned last year's beaten finalist and eighth seed Jelena Jankovic to book her place in the quarter-finals.
The 19-year-old American defeated the Serbian 6-4 0-6 7-5 despite trailing 3-1 in the third set.
Jackson next plays Russian fourth seed Elena Likhovtseva who beat American Lisa Raymond 7-5 6-4.
Italian second seed Francesca Schiavone came from a set down to beat Bulgarian Tsvetana Pironkova 3-6 6-3 6-1.
Jackson sealed a rollercoaster win
But Japanese fifth seed Ai Sugiyami and Russian seventh seed Anna Chakvetadze were both beaten in the third round by lower-ranked opponents.
A Wimbledon quarter-finalist in 2004, Sugiyami lost 7-6 (7-4) 6-4 to 12th seed Santangelo.
Chakvetadze, meanwhile, lost 6-4 6-3 to unseeded compatriot Vera Zvonareva, who has swept through her opening three matches.
After beating Anne Kremer of Luxembourg 6-0 6-1 and Slovakia's Martina Sucha 6-1 6-2, the 21-year-old completed another straight-sets win and now faces Schiavone.
Number six seed Marion Bartoli endured a 132-minute marathon before finally overcoming 16-year-old Ayumi Morita of Japan 6-4 5-7 6-2.