The 11th-ranked Italian needs to win the tournament as well as next week's Kremlin Cup in Moscow to qualify for the elite season-ending event.

Pennetta dropped serve three times and saved eight more break points while struggling against Groenefeld.

She next plays unseeded Ioana Raluca Olaru of Romania, who rallied to defeat German qualifier Julia Goerges 3-6, 6-2, 7-5.

Second-seeded Agnieszka Radwanska also advanced but younger sister Usrzula couldn't join her and set up a family clash.

Agnieszka Radwanska defeated Alize Cornet of France 6-4, 7-5 in the second round, while Urszula Radwanska lost to seventh-seeded Lucie Safarova of the Czech Republic 6-4, 6-4.

The Polish sisters would have met for the third time this year if they'd both won.

Instead, Safarova will go into the clash having beaten Radwanska in their only previous match in three sets more than two years ago,

Radwanska, coming off an outstanding trip to Asia where she reached the Tokyo semifinals and Beijing final, dictated the pace against Cornet from the baseline, breaking twice in the first set and three times in the second.

Safarova, the runner-up in Quebec last month, dropped serve early in the opening set before breaking back twice. She then broke once more in the second set.

Also moving on was No. 3 Yanina Wickmayer of Belgium, who rallied to beat Alexandra Dulgheru of Romania 2-6, 6-3, 6-1.

Wickmayer scored only one point against Dulgheru's serve in the opening set, but the U.S. Open semifinalist later broke the Romanian's serve six times.