NEW YORK, NY, USA - Friday afternoon at Flushing Meadows will see all four semifinalists in action. First up are Victoria Azarenka and Flavia Pennetta, before being followed on court by Li Na and defending champion Serena Williams.
Arthur Ashe Stadium
 Victoria Azarenka (BLR #2) vs. Flavia Pennetta (ITA #83)
Head-to-head: series tied 1-1
Twelve months ago, a tearful Flavia Pennetta was following the US Open from the comfort of her home as she recovered from a career-threatening wrist injury. On Friday, she will take on No.2 seed Victoria Azarenka in her maiden Grand Slam semifinal and, judging by her showings in the past few rounds, the Italian's feel good story could yet have a few more chapters.
Pennetta is still to drop a set this fortnight, with her sprightly movement, tactical intelligence and razor-sharp returning - she has broken serve 28 times - helping her to wins over Sara Errani, Svetlana Kuznetsova, Simona Halep and Roberta Vinci.
Despite her opponent's form, Azarenka, as ever, will not be lacking in self-belief. After coming through early tests against Alizé Cornet and Ana Ivanovic, the Belarusian once again appears to be peaking at the business end of a major. She produced her best performance of the tournament to brush aside Daniela Hantuchova last time out and will start as clear favorite to reach a second straight final at Flushing Meadows.
 Serena Williams (USA #1) vs.  Li Na (CHN #6)
Head-to-head: Williams leads 8-1
Li Na is faced with an unenviable task in the second of the semifinals: derailing the Serena Williams juggernaut. In five matches at Flushing Meadows, Williams has dropped just 13 games, with her five wins taking her record since the start of the year to 65-4.
Driving this form has been an imperious serving display that has seen the American broken just once, hitting 21 aces and winning 111 of 137 points on her first delivery. And the daunting statistics do not end there; in 23 major semifinals, Williams has only ever lost three times, with her conquerors the multiple Grand Slam winning trio of Justine Henin, Kim Clijsters and her sister Venus.
However, as Serena admitted earlier this week, Li has one of the most complete games on tour. And her full repertoire of skills have been on display in New York, with her serve particularly potent - she has hit a tournament-leading 29 aces - in powering her to a maiden US Open semifinal. This delivery will need to be on song once more if she is to register a rare win over Williams, who she has defeated just once in nine attempts.