NEW YORK, NY, USA - The screws tighten at Flushing Meadows on Sunday as the first quarterfinal berths go up for grabs. And it's a classy line-up, with four Grand Slam champions on the schedule - three of them former No.1s - as well as two former finalists.

Arthur Ashe
[2] Kim Clijsters (BEL #3) vs. Ana Ivanovic (SRB #40)
H2H: Clijsters leads 2-0
These two haven't had much luck finishing matches. One of Clijsters' wins came when Ivanovic retired with a foot injury three games into their recent semi at Cincy; she also got a walkover from the Serb at Toronto in 2005. So it's more than three years since they went the distance, Clijsters prevailing on an indoor carpet court at Antwerp. Whatever. One of the impressive features of Ivanovic's run this week has been the way she's closed out matches, twice winning the second set 6-0 - not bad for a player rediscovering form and confidence. Has she come along sufficiently to upset the defending champion and reach her first Grand Slam quarterfinal since her Roland Garros-winning run in 2008? This is probably Clijsters' to lose, but stranger things have happened.

[3] Venus Williams (USA #4) vs. [16] Shahar Peer (ISR #19)
H2H: Williams leads 5-0
Just as well these two like each other; this is the fourth time they've met this year, though Peer, who has never taken a set from the American, surely wishes she could make more of a dent. Maybe this is her chance - a fine third round win over Flavia Pennetta certainly augurs well, sitting on top of what has been a busy and productive season. For her part Venus has also advanced without incident, showing no ill effects of the injury that kept her out of action during the summer, but given her last two opponents were inexperienced qualifiers it is perhaps harder to gauge her true level. Given that 23-year-old Peer is playing her seventh fourth round match at a major, and aiming for a second US Open quarterfinal, things should be clearer by the end of this encounter.

[5] Samantha Stosur (AUS #6) vs. [12] Elena Dementieva (RUS #12)
H2H: Dementieva leads 4-1
After a patchy summer Stosur can be happy she's reached the fourth round of the US Open for the first time. And should she keep her run alive she'll be the first Australian woman to reach the quarters at Flushing Meadows since Wendy Turnbull in 1986. Don't be fooled by the low-key exterior - the 26-year-old wants that and much, much more, but Dementieva has proven a difficult foe in the past, winning all of their matches on hardcourts. Almost 29, the 2004 runner-up has been quietly gathering steam. Despite dropping from the Top 10 she is a respectable 3-2 against that elite this season, and arrived at Flushing Meadows having won 48.9% of return games played - best on Tour. Whoever wins this one will go up in the title contender stakes.

Louis Armstrong
[6] Francesca Schiavone (ITA #7) vs. [20] Anastasia Pavlyuchenkova (RUS #22)
H2H: Tied 1-1
Both are enjoying their best seasons, just at different stages of their careers. Payluchenkova, the highest ranked teenager, has won two hardcout titles this year - she is a Tour-leading 30-10 in main draw matches on the surface - and this week has already achieved her best Grand Slam result. Can the 2006 US Open junior champion keep it going? You bet she can, but a certain 30-year-old French Open champion will have other ideas. Interestingly, Schiavone's third round defeat of Alona Bondarenko was her first over a Top 50 player since Roland Garros, but maybe that's just what she needed to get back on track. She hasn't missed a major since she made her debut here in 2000... and won't want to leave this party just yet.

More to watch…
In third round doubles, No.2 seeds Liezel Huber and Nadia Petrova play Timea Bacsinszky and Tathiana Garbin on Louis Armstrong. Court 7 plays host to fifth-seeded doubles veterans Lisa Raymond and Rennae Stubbs, who face No.10 seeds Maria Kirilenko and Agnieszka Radwanska. Wimbledon champions Vania King and Yaroslava Shvedova, the No.6 seeds, play twelfth-seeded Iveta Benesova and Barbora Zahlavova Strycova on Court 11. Bethanie Mattek-Sands and Daniel Nestor, the No.4 seeds in the mixed event, play Aravane Rezai and Rajeev Ram on Court 4.