STUTTGART, Germany, Oct 2, 2008 (AFP) - Wimbledon champion Venus Williams will take on world number three Dinara Safina in the quarter-finals of Stuttgart's WTA event after her comfortable second-round win on Thursday.

The American needed a little over an hour and hit a staggering 12 aces as she over-powered Ukraine's Kateryna Bondarenko 6-4, 6-2 to set up Friday's last-eight clash with French Open runner-up, and Olympic silver medallist, Safina.

The first set was fairly close as Williams had her service broken and had to break back before sealing the opener 6-4, but the second was one-way traffic as Williams blasted eight aces, while Bondarenko replied with four double faults.

'The first set was tough, she broke me, so I had to break back and work hard,' admitted Williams.

'It was a good, hard game, but I felt comfortable on court and I am looking forward to the quarter-final.'

Earlier Russia's Olympic stars Safina and Vera Zvonareva produced impressive to book their quarter-finals places.

Safina had to work for her 6-1, 7-6 (8/6) win over Bulgaria's Tsvetana Pironkova, while Zvonareva, who won bronze in Beijing, dominated France's Marion Bartoli for a 6-2, 6-0 victory.

Having needed just 21 minutes to take the first set 6-1, Safina was made to work hard in the second as the 21-year-old, 49 places below her in the WTA rankings, took the set to a tie-break with a clever selection of shots.

Pironkova was regularly hitting her serves over 190km/h and smashed four aces in the second set, but Safina put her under pressure in the tie break and the Bulgarian's inexperience played into her opponents' hands.

'She's a good player, but I had plenty of opportunities to win the match,' said Safina.

'I became a little bit slow in the second after I dominated the first.

'I lost my concentration, but it was good to have a hard second set - it will help me for later in the week.'

Zvonareva made few mistakes and needed just 58 minutes for her straight sets win over Bartoli and will play either world number two Jelena Jankovic or Alona Bondarenko on Friday for a place in the semi-finals.

And 2006 winner Nadia Petrova is safely in the quarter-finals after her second round 6-4, 6-1 win over Switzerland's Patty Schnyder.

Petrova will play China's Li Na, who beat world number one Serena Williams on Wednesday, in the quarter-finals.