"You can never underestimate anyone, " said the second seed, who attended her news conference wearing a T-shirt emblazoned with the message, "Can't spell dynasty without nasty".

BBC: Serena and Venus battle through

"I had a great week of practice and I was ready to go, " said the big-serving Isner, who will be the second seed at this week's U.S. Men's Clay Court Championship.

CNN: STORY HIGHLIGHTS

"I stayed aggressive and made sure to have an extra something on my ball, " said fifth seed Sharapova, who will face second seed Elena Dementieva of Russia in the quarter-finals.

BBC: Marion Bartoli defeats Ana Ivanovic at Stanford Classic