Stuttgart, Germany -- (Sports Network) - U.S. Open runner-up Jelena Jankovic and Wimbledon champion Venus Williams led the charge into Saturday's semifinals at the $650,000 Porsche Tennis Grand Prix. Jankovic will become the new women's world No. 1 when the rankings are released on Monday.

The second-seeded Jankovic held off seventh-seeded Russian Vera Zvonareva in a pair of tiebreaks, 7-6 (10-8), 7-6 (7-5), on the indoor hardcourts at Porsche Arena. The capable Zvonareva captured an Olympic bronze medal in Beijing back in August.

Jankovic, fresh off her WTA Tour title in Beijing last week, will battle Williams here on Saturday. The Serb is 4-3 lifetime against the American, including a win in a quarterfinal in Rome earlier this season. Jankovic has won four of their last five meetings overall.

A sixth-seeded Williams upset French Open and Olympic runner-up Dinara Safina, of Russia, 6-4, 6-2. Safina was seeded third this week.

The former world No. 1 Venus is the reigning two-time Wimbledon champ.

Another upset came when promising Belarusian Victoria Azarenka posted her second victory over a Top-10 opponent this week by erasing Olympic gold medalist Elena Dementieva, of Russia, 7-6 (8-6), 3-6, 6-1. The two-time major runner-up Dementieva was seeded fourth here.

One other Day-5 bout saw Russian Nadia Petrova dismiss Chinese Na Li 6-2, 6-3. Li shocked top-ranked Serena Williams here on Wednesday.

Petrova will meet Azarenka in Saturday's other semi.

The 2008 Stuttgart titlist will take home $100,000.