Rafael Nadal will keep the No. 1 ranking for at least another week following an efficient 6-1, 6-3 win over Croatia's Marin Cilic in the Italian Open quarterfinals on Friday.
Nadal was in risk of losing the top spot to Novak Djokovic if he failed to reach the semifinals of this clay-court tournament, which the Spaniard has won five of the last six years.
Nadal played much sharper than in his previous two matches when he was affected by a virus. His semifinal opponent will be either seventh-seeded Tomas Berdych or 16th-seeded Richard Gasquet, who eliminated Roger Federer on Thursday.
In the other half of the draw, Andy Murray overcame a slow start to beat German opponent Florian Mayer 1-6, 6-1, 6-1 and become the first British man to reach the semifinals of this tournament in the Open era.
The fourth-ranked Murray also showed good clay-court form in Monte Carlo last month, taking a set off Nadal in the semifinals.
"If I want to get to No. 1 in the world then you need to play well on all of the surfaces because Roger, Rafa and Novak - they all play well on all the courts," Murray said. "I need to improve my game on the surface and it's been better this year."
The last British man to reach the semifinals at this event was George Hughes in 1932, while the last British player to win the title at the Foro Italico was Virginia Wade in 1971.
Hughes was the only British man to win the tournament in 1931.
"When we walk to the practice court they have a list of all of the winners down the wall and there is a lot of great players," Murray said. "It is nice and I want to try and go further."
Murray's semifinal opponent will be either Djokovic or Robin Soderling, who were playing in a night match.
Djokovic is on a 36-match winning streak and is undefeated this year.
In women's action, Australian Open runner-up Li Na of China beat Greta Arn of Hungary 6-3, 6-1. Na's semifinal opponent will be either defending French Open champion Francesca Schiavone or Sam Stosur, who were playing later in a rematch of last year's Roland Garrros final.