Rafael Nadal guaranteed he would become the third Spanish man to top the world rankings with a 7-6, 6-1 victory over Ecuador's Nicolas Lapentti in the quarter-finals of the Cincinnati Masters on Friday.
By beating Lapentti, Nadal will end Roger Federer's four-and-a-half-year reign as world number one on Aug. 18 at the latest, or as early as Monday if he takes the Cincinnati title.
"It was a tough match," Nadal said in a courtside interview.
"I was a little bit tired, especially after a tough win in Toronto last week. And the weather here is very humid and hot but it is important to be in the semi-finals.
"I am happy because I have been fighting a lot these last three years, although I was happy as number two as I won a lot of tournaments.
"But for sure, number one is a goal and I am very happy."
Nadal's win also took him a step closer to a sixth successive tournament triumph, underlining his evolution into a far more adaptable player on all court surfaces rather than his favourite, clay.
After ending Federer's five-year winning run at Wimbledon last month, Nadal has maintained his superlative form on the hard courts of North America while his Swiss rival has stumbled to early defeats in the two tournaments he has played since.
Should Nadal lose Sunday's final he would top the rankings on Aug. 11 while a semi-final defeat would delay his coronation for another week.
The 32-year-old Lapentti took the contest to a tentative Nadal in the first set, often pinning the Spaniard way back behind the baseline with an aggressive brand of attacking tennis.
Nadal saved two break points in the eighth game and the reprieve appeared to invigorate him into action as he cruised through the tiebreak and the second set to seal victory in a one hour and 48 minutes.
The number two seed will face Novak Djokovic in Saturday's semi-final after the Serb battled past unseeded Latvian Ernests Gulbis 6-3 6-4 and Nadal knows he will need to play better to advance.
"If I want to beat Djokovic I have to play better than today and have to play my best match in Cincinnati for sure."
Saturday's other semi-final will be contested by eighth-seeded Briton Andy Murray, who rallied past Spain's Carlos Moya 2-6 6-3 6-1, and 16th seeded Croatian Ivo Karlovic, a 7-6 7-6 winner over Philipp Kohlschreiber of Germany.
Moya and Juan Carlos Ferrero are the other Spaniards to have topped the world rankings since they were first devised in 1973.