New York, NY -- (Sports Network) - World No. 1s Rafael Nadal of Spain and Ana Ivanovic of Serbia learned the paths they'll have to take en route to the finals, as the 2008 U.S. Open draws were announced on Thursday.

The Open will commence Monday at the USTA Billie Jean King National Tennis Center.

The reigning Wimbledon, French Open and Olympic champion Nadal could meet American James Blake in the quarterfinals and fellow Spaniard David Ferrer in the semis in a tough top half of the men's draw. His opponent in the final could be Federer, who was replaced atop the world rankings by Nadal just this week. Nadal had been No. 2 for a record 160 straight weeks, while Federer was No. 1 for a record 237 consecutive weeks.

This will mark the first time that Nadal is the top seed at a Grand Slam event. The Spaniard will try to become the first man to win the French Open, Wimbledon and the U.S. Open in the same year since Aussie legend Rod Laver turned the trick back in 1969.

Nadal will open his "Big Apple" stay against a qualifier.

The reigning four-time U.S. Open champion Federer could meet Australian Open champ Novak Djokovic in the semifinals, which would mark a rematch of last year's title tilt, won by the 12-time Grand Slam champion from Switzerland.

Federer will open up against Argentine Maximo Gonzalez, while Djokovic will take on Frenchman Arnaud Clement, a Wimbledon quarterfinalist last month.

A struggling Federer has dropped four of his last eight matches and lost to Nadal in the French Open and Wimbledon finals. The Swiss great was the reigning five-time Wimbledon champ when he succumbed to his Spanish rival in an epic encounter at the All England Club.

Former U.S. Open champ Andy Roddick, seeded eighth at this particular fortnight, will open up against French veteran Fabrice Santoro and could meet Djokovic in the quarters.

On the women's side, the French Open champion and Aussie Open runner-up Ivanovic could meet surging sixth-seeded Russian Dinara Safina in the quarterfinals. Ivanovic beat Safina in the French Open final back in June. Safina was last week's silver medalist at the Beijing Olympic Games.

Ivanovic, who will open up against Russian Vera Dushevina, could battle second-seeded fellow Serb Jelena Jankovic in the women's final. Jankovic's first-round opponent will be American Coco Vandeweghe.

The mighty Williams sisters could square off in the quarterfinals in Flushing. Venus will open up against Aussie Samantha Stosur, while Serena will take on Ukrainian Kateryna Bondarenko in the round of 128.

The seven-time Grand Slam titlist Venus is a two-time U.S. Open champ and the reigning two-time Wimbledon titlist, while the eight-time major champion Serena is also a two-time U.S. Open winner. The former world No. 1 sisters met in last month's Wimbledon final, with Venus prevailing for a repeat performance in Britain.

Retired Belgian Justine Henin beat 2004 titlist Svetlana Kuznetsova in last year's Open final. A third-seeded Kuznetsova will open against a qualifier next week.

Olympic gold medalist Elena Dementieva will open against Uzbekistan's Akgul Amanmuradova and could tangle with her fellow Russian Kuznetsova in the quarters.