Rafael Nadal lost his long unbeaten streak on clay and his world number one ranking after a shock defeat to Dominic Thiem in the Madrid Open quarter-finals.
The Spaniard had surpassed John McEnroe's record for 50 straight-set wins on a single surface when he eased through to the last eight of the event on Thursday.
But Nadal could not maintain his form and went down 7-5 6-3 to the Austrian world number seven, who broke his opponent's serve five times in the two-hour match.
As a result of Nadal's defeat, Roger Federer, who is sitting out the clay-court season, will return to world number one on Monday, but Nadal could regain top spot with a win in Rome.
Nadal told atptour.com: "I am playing against one of the best players in the world and we were playing in special conditions - the ball flies more here and i was not under control of the point.
"I tried to come back but I wasn't good enough today. I think I've placed myself in a good position. I still have two good weeks on clay then I'll keep moving forward."
In the semi-finals, Thiem will face South African sixth seed Kevin Anderson, who proved too strong for Serbian qualifier Dusan Lajovic, winning 7-6 (7/3) 3-6 6-3 in just over two hours.
Kyle Edmund's run came to an end at the quarter-final stage as he was beaten by Canada's Denis Shapovalov.
Edmund saved a match point at the end of a feisty second set which also involved an incident in which the British number one was distracted by a spectator.
But he could not hold off his 19-year-old opponent who broke early in the third and served well to triumph 7-5 6-7 (7/6) 6-4.
Edmund will take heart from his week, though, especially his memorable win over Novak Djokovic in the earlier rounds.
In the last four, the Canadian will face world number three Alexander Zverev, who repelled big-serving American John Isner 6-4 7-5.
The 21-year-old Zverev did not face a single break point in the course of his 78-minute victory, and one break of the Isner serve in each set proved sufficient to see him through.