Federer, Serena, Venus advance

Serena and Venus Williams and men's world number two Roger Federer cruised into the fourth round of the WTA and ATP hardcourt tournament here on Sunday but second seed Dinara Safina crashed out.

Reigning Australian Open champion Serena Williams defeated China's Peng Shuai 7-5, 6-2 while US fifth seed Venus Williams, the reigning Wimbledon champion, beat Germany's Anna-Lena Groenefeld, 7-5, 6-3.

The sisters could meet in a semi-final at this nine million-dollar event, which saw its greatest upset yet when Australia's 42nd-ranked Samantha Stosur stunned Russian second seed Safina 6-1, 6-4.

"I'm really happy," Stosur said, "I played really well. I executed exactly what I wanted to do." Safina could have become the women's world number one by winning the title.

"It's very disappointing. That's what I'm playing for," Safina said. "I want to be there. Suddenly I go to the court and I don't even fight for it. It's just bad behavior from my side. Champions, they don't do this. "It's a good punishment for me. I have to get smarter."

Swiss star Federer, a Miami champion in 2005 and 2006, advanced by beating German 28th seed Nicolas Kiefer 6-4, 6-1 to book a fourth-round match against American Taylor Dent, who beat Spanish 15th seed Tommy Robredo 7-5, 6-3.

MIAMI, Florida, Tuesday, AFP