Arthur Ashe Stadium
 Li Na (CHN #6) vs.  Ekaterina Makarova (RUS #25)
Head-to-head: Li leads 3-0
The statistics do not augur well for Ekaterina Makarova's chances of making it past Li Na and into the semifinals in New York; she is 0-3 head-to-head against Li and her two previous ventures this far at a major - at the Australian Open in 2012 and 2013 - have both ended in straight set defeats.
However, after recovering from the loss of the first four games to defeat No.3 seed Agnieszka Radwanska in the last round, Makarova will not be lacking in confidence when she steps out on Ashe.
Li will present a different set of challenges and the Russian's lefty serve out wide and big forehand will have to be firing on all cylinders once again. Like Makarova, Li has been playing arguably her best tennis of the season in the opening four rounds, and if she can maintain the form that took her past Jelena Jankovic for the loss of three games, she will fancy her chances of not only making the semifinals but going all the way to the title.
 Serena Williams (USA #1) vs.  Carla Suárez Navarro (ESP #20)
Head-to-head: Williams leads 2-0
Two days before turning 25, Carla Suárez Navarro delivered a coming of age performance to knock out No.8 seed Angelique Kerber and reach the quarterfinals of the US Open for the first time. However, as brilliant and belligerent as her play was against Kerber, she will need to up her level again if she is to dethrone reigning champion Serena Williams.
In Williams, she is taking on a player at the very top of her game. Since losing in the first round of last year's French Open, the American has embarked on arguably the most consistent run of her career, capturing 13 titles - three of them Grand Slams - and losing just five times. There has been no let up at Flushing Meadows, where Williams has looked hungry for a fifth US Open title, dropping a mere 13 games so far.
Suárez Navarro's progress has not been quite so serene, with her fourth round epic against Kerber taking her total time on court past the six hour mark. Williams has won both of the players' past encounters in straight sets - the most recent coming in Rome a few months back - and the Spaniard must serve well and stay loose, particularly on her signature backhand, if she is to stand a chance of causing the upset.