The Open, the year's final major tournament for tennis, runs over the next two weeks. World No. 3 Andy Murray is the defending champion.
Murray and top-ranked Novak Djokovic have played in three of the last four major finals.
Murray won last year's U.S. Open and Wimbledon this year. Djokovic, in January, claimed his third consecutive Australian Open title.
What those tournaments didn't have was a healthy Nadal in the field. He didn't play at all in the 2012 U.S. Open or Australia and lost in the first round in Wimbledon. He won the 2013 French Open -- for an eighth time overall and fourth in a row -- defeating David Ferrer in the final.
What the 2013 U.S. Open has is an apparently healthy Nadal. He's 10-0 with two tournament titles since the Wimbledon loss and ensuing five-week layoff to rest his knee. Since February, Nadal is 53-3 with nine tournament championships and two runner-up finishes in 13 events.
A win in the men's singles final Sept. 9, would give Nadal a second U.S. Open title (the first was in 2010) and mark his 13th Grand Slam championship. Only Roger Federer (17) and Peter Sampras (14) have won more.
There are scenarios in which Nadal can pass Djokovic, who has been No. 1 for the last 43 weeks, for the rankings' top spot. If Djokovic is in the final, he retains the top ranking. But if Djokovic is ousted in New York before the quarterfinals and Nadal reaches the final, Nadal is No. 1. If Djokovic advances to the semifinals, Nadal needs to win the tournament to take over the top spot.
Nadal was most recently No. 1 in the rankings July 3, 2011. He's had two spells at the top, totaling 102 weeks, which is seventh most overall. Djokovic has been on top 96 weeks; Federer owns the record with 302.
There were no changes in the Top 10 this week. Jurgen Melzer defeated Gael Monfils in Saturday's final of the Winston-Salem Open. It was his fifth career title and moves him up five places in the rankings to No. 27. Monfils goes from 43rd to 39th.
The ATP Top 10 heading into the U.S. Open, listing player, home country, rankings points and points won in the 2012 U.S. Open:
1. Novak Djokovic, Serbia, 10,980 (1,200, runner-up)
2. Rafael Nadal, Spain, 8,860 (0, did not play)
3. Andy Murray, Great Britain, 8,700 (2,000, champion)
4. David Ferrer, Spain, 7,210 (720, semifinalist)
5. Tomas Berdych, Czech Republic, 5,075 (720, semifinalist)
6. Juan Martin del Potro, Argentina, 4,740 (360, quarterfinalist)
7. Roger Federer, Switzerland, 4,695 (360, quarterfinalist)
8. Jo-Wilfried Tsonga, France 3,470 (45, second round)
9. Richard Gasquet, France, 2,625 (180, fourth round)
10. Stanislas Wawrinka, Switzerland, 2,610 (180, fourth round)