The 2013 U.S. Open might be more than just a tough test for the top tennis stars.
It could very well be a test they fail before the quarterfinals.
Surprise losses happen in every Grand Slam. In New York, there have been downright shocking results in the early rounds over the years.
Just ask Andre Agassi.
In 2000, Agassi was the defending champion and ranked No. 1 in the world. Those credentials weren't enough to stop him from losing to No. 37 Arnaud Clement in the second round, 3-6, 2-6, 4-6.
Or what about Ana Ivanovic? She was also the No. 1 player, but she also lost in the second round. Ivanovic was done in by qualifier Julie Coin, ranked No. 188, 3-6, 6-4, 3-6, in the 2008 Open. Richard Pagliaro of Tennis.com regarded it as one of the most shocking upsets of U.S. Open history.
Could that happen to a top player this year?
There are some surprising head-to-head records on the resumes of the top four men's and women's stars. Each has the chance to face an opponent before the quarterfinals that they just don't match up well against.
Rafael Nadal and Agnieszka Radwanska, for example, have losing records against much-lower-ranked players that they might run into.
That's more than enough to explain Nadal's dour expression.
Time to explore some intriguing tests.