Serena Williams eased into the second round of the Bank of the West Classic with a straight sets defeat of Li Na.

The Wimbledon champion saw off her Chinese opponent 6-3 7-6 in the 700,000-dollar WTA Tour event at the Taube Family Tennis Center in Stanford.

Williams' elder sister, Venus - who she beat in the final at SW19 earlier this month - was a comfortable 6-2 6-3 winner against Canada's Stephanie Dubois, while Germany's Sabine Lisicki knocked out Lilia Osterloh by the same margin.

Slovakia's Daniela Hantuchova needed three sets to see off Canada's Aleksandra Wozniak, the defending champion, 6-4 4-6 7-5.

It was a similar story for Russia's Maria Kirilenko, who downed compatriot Anna Chakvetadze 6-4 5-7 7-6.

In other matches, Serbia's fourth seed Jelena Jankovic beat America's Angela Haynes 6-3 6-1, eighth seed Marion Bartoli of France knocked out Japan's Ayumi Morita 7-6 6-3 and Australia's Samantha Stosur defeated Slovakia's Dominika Cibulkova, the sixth seed, 6-4 6-3.