Li Na will be looking to beat Williams for the first time in five years (GEOFF ROBINS/AFP/Getty Images)
Serena Williams looks pretty much unstoppable this week but does defending champ Li Na have any chance? Watch this semi-final live online.
Williams says she hasn't been feeling especially comfortable in the conditions this week and she did drop a set to Eugenie Bouchard in her opening match, so maybe Li might have half a chance.
However the top seed has lost to just three players all year while amassing eight titles and she looked formidable during her 6-0, 6-4 quarter-final demolition of Simona Halep especially in the first set where she produced near perfect tennis. Having said that, Williams was definitely far below her best in the Rogers Cup semi-finals last week where she had to fight extremely hard to see off Agnieszka Radwanska in straight sets.
Li won the Cincinnati title twelve months ago and she'll be taking heart from the fact that Williams has never made the final of this tournament before. She hasn't played a match in two days after Radwanska pulled out before their quarter-final clash in order to attend the funeral of her grandfather.
However the Chinese star produced some impressive tennis earlier in the week, fighting back to beat the talented young American Lauren Davis in three sets before outplaying Angelique Kerber 6-4, 6-4.
Williams says that having had a day off will make no difference to the quality of Li's tennis.
"She's a really tough player whether she had a day off or a three or five set match today. She's so fit, she would be ready to play just as tough tomorrow. So that doesn't matter. It will be a really tough match because she has such a good game and she does everything so well."
Williams has won seven of her eight matches against Li but every one of their matches has been tightly contested. Li has not beaten her since 2008 with Williams finding a way through in their past six encounters. They met in the Miami quarters earlier this year with Williams winning 6-3, 7-6(5) on the way to the title.