Rome, Italy -- (Sports Network) - Second-seeded Maria Sharapova advanced, while both Williams sisters exited the quarterfinal round of the $1.34 million Italian Open on Friday, a clay-court French Open tuneup.

Fifth-seeded Serena Williams pulled out due to a back injury, and seventh- seeded Venus Williams came up a loser at the hands of defending champion Jelena Jankovic.

Sharapova dropped the first set, but rebounded to earn a 6-7 (3-7), 7-5, 6-2 win over Patty Schnyder, in just under 2 3/4 hours. The Australian Open champion Sharapova will become the new women's world No. 1 when the rankings are released on Monday.

Meanwhile, the fourth-seeded Jankovic came from behind to beat Venus in 5-7, 6-2, 6-3 fashion at Foro Italico. The 2007 Wimbledon champion Venus, the 1999 Rome titlist and 1998 runner-up here, was playing her first tennis in a month after taking some time off due to medical reasons.

Jankovic captured this event last year by beating Russian Svetlana Kuznetsova in the finale.

Serena decided against playing her quarterfinal on Day 5 because of a back problem, thus giving French qualifier Alize Cornet a walkover in Saturday's semifinals.

"It just happened all of a sudden in practice," Serena said about her back. "I just went for a shot and then my back got a little stuck."

Serena was the Rome champion back in 2002.

Another quarterfinal result saw sixth-seeded Russian Anna Chakvetadze hold off Bulgarian qualifier Tsvetana Pironkova 6-2, 3-6, 6-1. Chakvetadze will appear in only her second career semifinal on clay when she meets Cornet here on Saturday.

This year's Rome titlist will collect $196,900.