Williams has already beaten Li twice in 2013 (Photo by Clive Brunskill/Getty Images)
Serena Williams has been superb so far but can Aussie Open finalist Li Na give her a challenge in Friday's semi-finals?
Williams has dropped a miserly thirteen games in five matches en route to the last four and looks virtually unbeatable right now. Sloane Stephens has been the only player who's been able to get close to her so far, pushing her hard during the first set of their fourth round match but once Williams took it, she quickly pulled away to a straight sets victory.
She sent a strong message to the players left in the draw with her 6-0, 6-0 quarter-final obliteration of Carla Suarez Navarro which was so one-sided, one couldn't help but feel pity for the Spaniard especially when Williams marched into the press room after the match and told the media that there was still room for improvement.
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Despite her success on the hard courts of Australia in the past, Li has never previously played that well at the US Open and this is the first time she's reached the semi-finals. She was unstoppable on the way to the quarter-finals, taking out 2012 conqueror Laura Robson in straight sets and battering former finalist Jelena Jankovic for the loss of just three games in the last sixteen.
She was given a far tougher test in the quarter-finals by giant killer Ekaterina Makarova. For a while it looked like the Russian might notch up another scalp but Li managed to pull through 6-4, 6-7(5), 6-2.
Williams has won eight of her nine matches against the Chinese star but they've contested a couple of close matches in 2013. Williams won 6-3, 7-6(5) in Miami and it was extremely close in Cincinnati a few weeks ago, the American edging it 7-5, 7-5 and she has plenty of respect for Li, saying:
"She's a great challenge. She moves really well. She does everything well. I think the challenge of playing someone like her is how do you beat a player that does everything so well? I'm going to have to, in the next couple days, think about that and come up with an answer to that. I'm having a blast this week. I have just really been enjoying my matches. For me, I have to stay in that moment of fun but intensity but calm. If I can try to do those three things, it works out."