Five storylines to watch this week

• Can Melanie Oudin keep it up? When Oudin took out Russia's Anastasia Pavlyuchenkova, a former junior champ, in Round 1, it was a solid win. When Oudin stared down Elena Dementieva, the fourth seed, in Round 2, it was a sterling upset by a fresh, young face and the best American not named Williams. By the time she beat Maria Sharapova in Round 3, Oudin was suddenly being hailed as a real contender.

While that might be a stretch, this event has doubled as Oudin's cotillion. The toast of Week 1, she plays with aggression that belies her size. (Ladies and gentlemen, start your Justine Henin comparisons.) She moves beautifully. And best of all, she savors the battle.

The hype machine and the eagerness (desperation?) for a next American star will be a mixed blessing to Oudin. But there sure is a lot to like here, starting with a winnable match against Nadia Petrova in Round 4.

GALLERY: OUDIN AT THE U.S. OPEN

• Can anyone stop the Fed Express?Roger Federer hasn't lost at the U.S. Open since 2003. He's won the last two majors and the last hard-court tune-up, Cincinnati. His draw was fortuitous. And thanks to CBS' preference, he's been scheduled for day sessions this weekend, avoiding the type of late-night sessions that thrill fans but mess up a player's schedule.

There are still four rounds of tennis to be played, but Federer could scarcely have scripted this event better. Barring a herculean performance, all signs suggest we're looking at Federer's sixth straight title in New York.

• Will the last remaining women's seed please turn out the lights? We knew women's tennis was (euphemism alert) "in flux" before the tournament, but this event has laid bare just the fragility of so many cast members. Consider that among Petra Kvitova (ranked 72), Yanina Wickmayer (50), Gisela Dulko (40) and Kataryna Bondarenko (52), one will be a semifinalist.

The good news? The unpredictability has yielded some gripping drama. Kvitova's win over top-ranked Dinara Safina will not go down as a classic, but it sure didn't lack for drama. The shaky state of affairs has greased the skids for Kim Clijsters (who's looked as good as ever) and fueled the Henin comeback rumors. It also means that Serena Williams can win her third major title of the year, thus installing some order in the women's game.

• How are the knees? Superior tennis will ultimately determine the championship. Superior health will matter as well. Specifically, how will Rafael Nadal's knees hold up? At full strength, Nadal is, of course, a threat to unseat Federer (and win the Career Slam in the process). He has looked both stellar and mediocre, winning his first three rounds, but not always showing full faith in his movement. If his knees hold up and his abdominal injury doesn't worsen, this could get interesting.

• Can the ridiculously nice weather hold up? While the weather is usually the stuff of inane small talk, it's having an outsized effect on the tournament. The perfect temperatures and climate -- pleasant, not too humid, no rain -- has been a boon for the fans as well as for the USTA, which will make its usual eight-figure profit, recession be damned. But the conditions have also been conducive to superb tennis. There have been very few withdrawals or retirements or matches ruined when Player A cramps or Player B suffers heat stroke. After last year's debacle during the final weekend, Mother Nature owed the U.S. Open. And she's made good on her debts so far.