Aug. 2 (Bloomberg) -- Rafael Nadal guaranteed an end to Roger Federer's record 4 1/2 year run as the top-ranked men's tennis player by reaching the Cincinnati Masters semifinals.

The 22-year-old Spaniard beat Nicolas Lapentti 7-6 (7-3), 6-1 last night to ensure that he'll replace Federer atop the rankings this month, the ATP said. The change could come as early as tomorrow if he wins the Cincinnati final.

If Nadal doesn't win the title, he would top the rankings on Aug. 11, while a defeat in today's semifinal against Novak Djokovic would delay his ascendancy another week, the ATP said. He'll join Carlos Moya and Juan Carlos Ferrero as Spanish men to be No. 1 since the rankings were introduced in 1973.

``Right now I know I'm going to be No. 1 and I'm very, very happy to be No. 1,'' Nadal said on the tournament's Web site. ``It's a present for a lot of work in the past.''

Nadal has won a career-best 32 consecutive matches and is two victories from taking his sixth straight title. His last defeat came at the hands of Ferrero on May 7 in Rome.

Federer, who lost to Nadal in five sets in July's Wimbledon final a month after falling to him in straight sets in the French Open championship match, has been No. 1 for 235 weeks.

His position as No. 1 was put in peril by early exits in Toronto and Cincinnati, as the tour switched to the hard courts of North America.

The 26-year-old Federer, a 12-time Grand Slam champion, has held the top spot in the rankings since Feb. 2, 2004, when he replaced Andy Roddick. He broke Jimmy Connors's 30-year-old record of 161 weeks atop the rankings in February 2007.

Federer next travels to Beijing for the Olympics before heading to the U.S. Open. If he fails to win in New York, it will be his first year without a Grand Slam title since 2002.

To contact the reporter on this story: Dan Baynes in Beijing at dbaynes@bloomberg.net

Last Updated: August 2, 2008 00:18 EDT