Asked at the post-match press conference, where she again looked unhappy, why she had had tears in her eyes on court, she replied curtly, "Because it was a hard match".
Juan Martin del Potro said that he was battling illness after he suffered a shock defeat in the China Open final on Sunday, losing 6-4, 6-4 to unseeded Nikoloz Basilashvili of Georgia.
Osaka's shock triumph - at such a young age and against one of the greatest tennis players of all time - propelled her into the limelight. "It's exciting to feel like I'm playing well at the end of the year", world number two Wozniacki said.
That's basically why." Osaka, who is still overcoming the tiredness post the US Open further added, "I just kind of felt a little bit exhausted practising and warming up for the match.
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I think opponents with much more potential than us finished behind us. "It is the life I love and since I was a kid I work for this".
"I think I played really well, probably the best match for me in the tournament".
The German spit out 31 unforced errors to 16 for her opponent, who notched 6 aces and 93 percent of her first service points overall to seal the win in just over one hour.
"I also want to thank and apologise to Anastasija for today".
If she wins against Wozniacki, Sevastova will rise to world number 11 but only to world number 12 if she loses. In the men's quarter-finals, the Italian Fabio Fognini continued his march towards a fourth title of the season with a 6-4, 6-4 victory over Marton Fucsovics of Hungary.