Nadal will have to wait until 18 August to take over as world number one
Novak Djokovic beat Rafael Nadal 6-1 7-5 to reach the final of the Cincinnati Masters and bring an end to the Spaniard's 32-match unbeaten run.
Serb Djokovic will meet Britain's Andy Murray in the final on Sunday.
Nadal, who will soon replace Roger Federer as world number one, went into the semi-final suffering from blisters.
"Probably I wasn't 100%," said Nadal. "During all of this tournament, I didn't play my best. I congratulate him because he's playing well."
Australian Open champion Djokovic - who has defeated Nadal in four of their six matches on hardcourt - made quick work of a weary Nadal, firing four aces and winning 76% of second-serve points.
He broke Nadal's opening two serves to go 5-0 up before taking the first set in less than 30 minutes.
Nadal made a fight of it in the second, carving out a break point at 3-2, but Djokovic saved it with a fierce forehand.
Five games later Djokovic made the crucial break after a series of brilliant baseline rallies before closing out the match.
Djokovic said: "No-one is unbeatable but the way he was playing we all thought he's not going to lose any time soon.
"I tried not to think of his winning streak and what his new ranking spot will be. I tried just to focus on my game.
"It was my intention to have a fast start and to step in and go for it. And in the second set I just tried to stay with him."
Nadal added: "I played the best summer hard season in my life, so I'm very happy for that," said Nadal, who is 64-8 on the season with seven titles.
"Today he played unbelievable in the first set. In the second set I felt well and in some moments I felt I was playing better than him, but finally, he beat me."
By reaching the semi-finals of the event, Nadal piled up enough points to overtake Roger Federer as the world's number one player.
Given the way points accrue - the last 52 weeks are counted - he will surpass Federer in the 18 August rankings.