Madison Keys of the United States saved a match point on her way to stunning No.2 seed Iga Swiatek 5-7, 6-1, 7-6(8) in the Australian Open semifinals, advancing to the second Grand Slam final of her career following the 2017 US Open.
Taylor Fritz and Madison Keys put Team USA into the United Cup City Finals after posting straight-set wins over Germany on Monday.
The win also marked the 40th WTA Tour singles final of Kvitova's career. Kvitova, who is 29-10 in finals, will aim for her 30th career singles title on Sunday.
Keys next faces Veronika Kudermetova or qualifier Ludmilla Samsonova, who meet in an all-Russian clash on Thursday.
On Sunday, Williams entered the US Open quarters for the 16th time in her career with a straight-set win over Petra Martic of Croatia at an electric Arthur Ashe Stadium.
Medvedev clinched his maiden Masters shield in Cincinnati, extending a dominant run that saw him reach three finals in three weeks.
Kerber moves on to the third round, where she will face either Saisai Zheng of China or Australia's Ashleigh Barty.
Later Wednesday, Osaka was joined in the record books by compatriot Kei Nishikori who reached his third semi-final at the US Open.
In the quarterfinals, Madison Keys will face the winner of the match between Taiwanese Su Wei Hsieh and German Angelique Kerber.
Sloane Stephens, sidelined for 11 months by a left foot injury until returning in July, captured her first Grand Slam title by routing fellow American Madison Keys 6-3, 6-0 in US Open final.
