Monday, Fourth Round
Arthur Ashe Stadium
Tsvetana Pironkova (BUL #55) vs.  Ana Ivanovic (SRB #13)
Head-to-head: series tied 1-1
Ana Ivanovic and Tsvetana Pironkova arrived in New York without a win between them on a North American hardcourt this summer. But after two quietly impressive first weeks, one of them is guaranteed to contest a US Open quarterfinal for the first time. Who it will be, though, is still very much up in the air.
The players have met twice before, although with the most recent of these coming over four years ago - a three set win for Pironkova in Rome - not much can be gleaned from previous sparring. Both players hit a relatively flat ball, and while the edge in pace may lie with Ivanovic, Pironkova's penchant for mixing up the spins, speeds and trajectories of her attack can neutralize any power disadvantage.
Andrea Hlavackova (CZE #82) vs.  Serena Williams (USA #4)
Head-to-head: first meeting
Prior to this week Andrea Hlavackova had never been beyond the second round in her six Grand Slam appearances. At No.82 in the world, the Czech is the lowest-ranked player left in the draw, but she has made a mockery of this number in the first week, scoring impressive wins over Klara Zakopalova and Maria Kirilenko.
If this breakthrough run is to continue, she will have to do something that has proved nigh on impossible this summer: defeat Serena Williams. Since her shock first round exit at Roland Garros, Williams has compiled a 22-1 win-loss record, picking up the Wimbledon, Stanford and Olympic titles along the way. The American starts as heavy favorite, although Hlavackova, whose previous two matches have each lasted nearly three hours, is unlikely to go down without a fight.
 Roberta Vinci (ITA #19) vs.  Agnieszka Radwanska (POL #2)
Head-to-head: Radwanska leads 4-0
In her 13 years on the WTA, Roberta Vinci has never been in a Grand Slam quarterfinal. In fact, before this year's Wimbledon she had never even made it beyond the third round. However, the stylish Italian has been playing some of the best tennis of her career during the summer hardcourt season, and if she replicates the dominant showing that saw Dominika Cibulkova swatted aside in the last round she is more than capable of breaking new ground this fortnight.
If she is to do this she will have get past fellow on-court artisan and World No.2 Agnieszka Radwanska. Despite arriving in Flushing Meadows a bit short of match practice after a few injury worries, Radwanska has played herself into form in the first week and looked particularly good defeating a resurgent Jelena Jankovic in the last round. The head-to-head record between the two is 4-0 in favor of the Pole, although all bar one of these have been tight affairs, with the most recent coming in Madrid earlier this year.
Around the grounds?
The day's other fourth round match sees Vinci's compatriot and doubles partner Sara Errani take on last year's semifinalist Angelique Kerber, while in the doubles the Williams sisters continue their quest for a third US Open crown with a tricky third round against Nadia Petrova and Kirilenko.