At the age of 31, Serena Williams is arguably playing the best tennis of her career, and there is no question that she is the best female player in the world. She has to win the U.S. Open to validate her fantastic season, though, and she must get past Li Na in the semifinals to have that opportunity.
While Li's resume pales in comparison to Serena's, she is the No. 5 player in the world and a Grand Slam winner in her own right. She also happens to be quite proficient on hard courts, so Williams will have her hands full. Most fans figured that Serena vs. Victoria Azarenka in the final was a foregone conclusion, but Williams can't afford to look ahead just yet.
Here is a breakdown of the biggest keys that Serena must follow in order to defeat her game opponent on Friday and reach the U.S. Open final.
Serena has many advantages over her opponents, but none is more glaring than her serve. Williams' power is unlike anything that has ever been seen in women's tennis, and she often uses it to outclass her opponents.
Li can't measure up to Williams in that regard, but she is a powerful player in her own right. Serena's second serve is better than the first serve of many players on tour; however, Li has the skill set to make Williams pay if she doesn't get her first serve in with regularity.
That wasn't a problem in Serena's most recent match against Carla Suarez Navarro as she connected on nearly three-quarters of her first serves. Williams also won an incredible 88 percent of her first-serve points, which shows how important Serena's serve can be.
With numbers like that, it wasn't surprising that Williams came out on top in a 6-0, 6-0 drubbing, which was the first Grand Slam double bagel since 1989, according to ESPN Stats and Info.
Serena won't be able to push Li around as much as Suarez Navarro since Li actually has some firepower in her repertoire, but the first serve remains key. If Williams is able to get 75 percent of her first serves in yet again on Friday, Li's chances of winning are low.
For Serena, it all comes down to personal execution. It is often said that Williams can only beat herself, and her first-serve stats will be very telling in that regard.
Limit Unforced Errors
Power players like Serena tend to go for winners in order to end points early and save energy for the remainder of the match. That used to be Williams' modus operandi, but she has grown significantly as a player over the years.
Serena still attacks and goes for winners when the time is right, but her conditioning is so good that she can engage in and win long rallies. One of the main reasons for her success these days is her willingness to allow her opponents to make mistakes.
She has been spectacular in all of her matches during the 2013 U.S. Open, but it makes sense to go back to her quarterfinal tilt with Suarez Navarro as it was essentially the perfect match. Williams only lost 18 points in the entire match, so it's natural that her unforced error total was low, but to have just nine as opposed to 20 winners is a huge accomplishment.
Having more than double the amount of winners than unforced errors is almost unheard of, but Serena pulled it off.
She is bound to make a few more mistakes against Li since the Chinese star will force her hand, but Serena has to make sure that she doesn't start spraying the ball around. That is when she becomes frustrated, and frustration makes her vulnerable.
Although Williams is 8-2 against Li with one of those losses being a walkover, Li has given her some problems. Serena won 7-5, 7-5 over Li in the Cincinnati Masters this year, which shows that there isn't a huge margin for error.
Attack Li's Second Serve
Li can more than hold her own against some of the sport's most powerful players due to her strong serve, but her second serve can definitely be attacked.
Few players in tennis are better at taking advantage of an opponent's second serve than Williams. Serena routinely blasts forehand winners off predictable second serves, and there is no question that she'll be looking to do that on Friday when Li puts herself in those types of situations.
Suarez Navarro witnessed Williams' proficiency at attacking second serves firsthand as Serena won 81 percent of the Spaniard's second-serve points.
Li's most recent match was far more difficult as it took her three sets to get past Ekaterina Makarova, but it's worth noting that she won just 50 percent of her second serves. That is a respectable number, but there is little doubt that the percentage is going to go down against Williams if Li doesn't improve her first-serve percentage.
If Li can connect on roughly 75 percent of her first serves, she'll put herself in a decent position to pull off the upset. If she gets under 70 percent, though, the door will be wide open for Williams to earn some breaks.
Li probably won't be able to break Serena with great regularity, so her best chance of winning is likely to involve forcing some tiebreaks. If Williams eats Li's second serve for lunch, though, that won't be possible.
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