STUTTGART, Germany—Venus Williams reached the Porsche Grand Prix quarterfinals by defeating Kateryna Bondarenko 6-4, 6-2 Thursday, one day after sister Serena was beaten and lost her No. 1 ranking.

Jelena Jankovic won her first match since learning that she will regain the top ranking, defeating Alona Bondarenko 6-2, 6-0.

Williams, seeded sixth, served 12 aces and won in 66 minutes. She fell behind 3-1 but recovered to break serve twice in taking the first set.

Jankovic and Bondarenko traded breaks of serve at the start of the match. But after Jankovic broke...

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