London: Belgium`s Kim Clijsters knocked out 11th seed Ana Ivanovic of Serbia in straight sets in the third round of the Olympic tennis tournament Wednesday.
The unseeded Clijsters broke Ivanovic once in each set to secure a 6-3, 6-4 win.
Clijsters, 29, will face either Russia`s world No.3 Maria Sharapova or 15th seed Sabine Lisicki of Germany in the next round.
Clijsters, a former world No.1, has never reached a final at Wimbledon and last appeared in the semi-finals in 2006.
Earlier, Serena Williams thrashed Russian No.2 Vera Zvonareva 6-1, 6-0 under the roof on Centre Court in just 51 minutes.
Williams will play either Danish eighth seed Caroline Wozniacki or Slovakia`s Daniela Hantuchova in the quarterfinals.