Naomi Osaka could lose the world number one ranking after defeat by Belinda Bencic in the quarter-finals of the Madrid Open.
Reaching the last four would have secured Osaka's grasp on top spot for another week but her 3-6 6-2 7-5 loss to resurgent Swiss Bencic means Simona Halep can overtake her by winning the title.
Japan's Osaka has limited experience on clay but looked poised for a fine win when she served for the match at 5-4 in the decider only for Bencic to reel off three games in a row and book a clash with Halep.
The Romanian advanced via a 7-5 7-5 victory over Australia's Ashleigh Barty.
Defending champion Petra Kvitova also crashed out, the three-time winner being beaten 6-2 6-3 by Kiki Bertens in a rematch of last year's final.
Her semi-final opponent is Sloane Stephens, who defeated Petra Martic 6-4 6-3.
PA
