Naomi Osaka slumped to a shock Madrid Open exit as she was beaten in the quarter-finals by Belinda Bencic despite serving for the match at one point.

World number one Osaka launched a staunch defence of her form prior to the WTA Premier tournament, insisting that her Australian Open title is proof of a fine season despite a recent run of poor results.

However, the 21-year-old came unstuck against Bencic – who also beat Osaka at Indian Wells in March – with the world number 18 breaking serve twice in the third set, including at 5-4 down, to clinch a surprise 3-6 6-2 7-5 victory.

Osaka started well with a break of serve and, despite conceding a service game of her own, took control and cruised to a 6-3 first-set success, but a resilient comeback in the second saw Bencic seize upon three out of four break points to level proceedings.

"I'm just very relieved right now"@BelindaBencic gives her first thoughts after taking out Osaka for the second time this year. pic.twitter.com/ATm9SMTOh4

— WTA (@WTA) May 9, 2019

Bencic's stoic effort appeared to be a fruitless one when Osaka broke serve to make it 3-2 in the third set, only for the 22-year-old to remarkably pull level when she capitalised on some nervy serving from Osaka.

And, after holding serve to nudge herself ahead, the comeback was complete when Osaka – who also received a warning for slamming her racket into the clay – dropped a short shot into the net.

Down goes No. 1!@BelindaBencic knocks out Osaka, 3-6, 6-2, 7-5, to seal a semifinal berth at the @MutuaMadridOpen  pic.twitter.com/zi0p7cJG1D

— WTA (@WTA) May 9, 2019

While Osaka, struggling to hold onto her number one ranking, must now rally ahead of the French Open at the end of May, Bencic's focus will switch to a semi-final clash with Simona Halep.