Former World number one tennis star on Wednesday stated that sky is the limit for the 2018 US Open champion Naomi Osaka, adding that Japan should be proud of her.

Ahead of Osaka's match against World number two Angelique Kerber in the ongoing Women's Tennis Association (WTA) Finals, the 39-time Grand Slam champion said that the 21-year-old is an exceptional player as she can hit anything.

"First of all, she hits a heavy ball. She can hit anything. If she really wants it, the sky's the limit. Beyond the sky. She's an amazing player already. What is she, 20? She's exceptional. I think Japan should be very proud of her. I know America is very proud of her. We are. She's both. I think that's great," WTA quoted King, as saying.

Osaka had defeated 23-time Grand Slam champion Serena Williams 6-2, 6-4 in the 2018 US Open final. The match was marred with controversy as the American player had lost her cool after chair umpire Ramos handed over three code violations against her for allegedly receiving on-court coaching.

Reflecting on the same, King said she knew that Osaka, who stood focused, would surpass Williams as the former was playing better than the latter.

"Even with the Serena match, I knew she was going to win that match because she was playing better than Serena, and she was not going to let anything, nothing deter her from winning. I know it was tough, it was just crazy and chaotic, but in the end, she prevailed, and I knew she prevailed because she stayed focused," King added.

Seeded at number three, Osaka was the third player after Simona Halep and Angelique Kerber, to qualify for her first WTA Finals.

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