Li Na ousts Clijsters for quaterfinals

Li, ranked 17th, rallied to oust the 2005 Miami champion and will play her quarter match against Russia's Anna Chakvetadze, who defeated Italy's Maria Santangelo 6-1, 7-5.

Clijsters said she was nagged by back discomfort and unable to play her best.

"I just have to kind of focus, make sure that I have my practice time at home and then try to peak at tournaments. It's not easy because I'm physically just not capable of playing a lot of matches anymore in a row," said Clijsters.

The Belgian said Li Na, the top tennis medal hope for China in the 2008 Olympics, has the potential to crack the WTA's top 10.

"I do believe that she's definitely a top-10 player. I've always had really tough matches against her," she said, "The last two or three times I played her, she missed a couple of important points."

"I think that's where maybe she still gets a little bit nervous. But it's just a matter for her to get through one of those big ones. Then I think the confidence will automatically rise and she'll be up there."