(CNN) -- Kim Clijsters' blistering return to competitive tennis gathered pace on Thursday with a hard-fought victory over Svetlana Kuznetsova of Russia in Cincinnati.
On the comeback trail: Clijsters held on for an impressive victory over Svetlana Kuznetsova on Thursday.
Playing as a wildcard, the unseeded Belgian defeated French Open champion Kuznetsova 6-4 4-6 6-2 in her first event after a two-year break from the sport.
Clijsters, 26, will now face world number one Dinara Safina in the quarterfinals of the $2 million hard court tournament.
Clijsters' successful comeback comes as both Williams sisters were knocked out of the draw.
In searing heat, Venus Williams lost a three-set encounter to Flavia Pennetta, while her sister Serena received a code violation for racket abuse on her way to a 7-5 6-4 defeat at the hands of Austrian Sybille Bammer.
Italian Pennetta, who won last week's tournament in Los Angeles, now goes on to play Daniela Hantuchova, with Bammer set to face Jelena Jankovic in the last eight.
Clijsters' return to professional tennis began on Monday night with a straight sets win over 12th seed Marion Bartoli of France.
She quit the WTA circuit in 2007 to get married and gave birth to a baby daughter in February 2008.
She looked on her way to a comfortable victory with a set and 3-0 lead over Kuznetsova.
However, the Russian held her nerve on two break points and battled back to serve out the second set.
Clijsters took advantage of a ten-minute heat break to collect herself before breaking Kuznetsova early in the decider and holding on for an impressive victory.
The final last-eight clash will feature fourth seed Elena Dementieva against eighth seed Caroline Wozniacki after they won their third-round clashes against Sorana Cirstea and Melinda Czink respectively.