Venus Williams [Images] overwhelmed third-seeded Russian Dinara Safina 6-4, 6-2 to reach the semi-finals of the Stuttgart Grand Prix on Friday.

The sixth-seeded American was too strong and consistent for Safina, making just eight unforced errors in a high-quality match that took just one hour 16 minutes.

Williams will go on to face second seed Jelena Jankovic of Serbia, who won a two-hour struggle with seventh seed Vera Zvonareva [Images] of Russia [Images] 7-6, 7-6.

Jankovic, who will take over as world number one next week, took the first-set tie-break 10-8 only to drop her serve at the start of the second. She finally broke back in game eight and forced another tie-break with a similar outcome.

In the other half of the draw, Olympic [Images] champion Elena Dementieva fell to Victoria Azarenka of Belarus 7-6, 3-6, 6-1.

The unseeded Azarenka hit with real venom and was helped by a stream of errors from fourth seed Dementieva as she sealed victory in two hours 54 minutes on centre court.

Azarenka will play her semi-final against another Russian after Nadia Petrova brushed aside China's Li Na 6-2, 6-3, finishing off with a booming ace down the middle at the indoor event.

Petrova, the 2006 champion, should have a big advantage in terms of physical condition after Azarenka's exhausting match took everything out of her.

"I just kept fighting and it worked," Azarenka told reporters. "There were a lot of long rallies and my legs are now dead."

After two tight sets Azarenka ran away with the third, building a 5-0 lead before Dementieva belatedly reacted.

The Russian saved three match points on serve before holding and threatened to get one break back in the next only for three unforced errors to seal her fate.

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