After losing the 2015 Australian Open final, Maria Sharapova did not expect her career to continue beyond the 2016 Olympics in Rio.
German third Angelique Kerber was upstaged by Ekaterina Makarova, while defending champion Karolina Pliskova cruised in Cincinnati.
Alexander Zverev's 10-match winning streak was ended by Frances Tiafoe, who triumphed in three sets against the fourth seed on Wednesday.
Incoming world number one Rafael Nadal accounted for Richard Gasquet 6-3 6-4 in Cincinnati on Wednesday.
After beating Venus Williams in Cincinnati to record her first win over a top-10 player, Ashleigh Barty was understandably thrilled.
Another stellar name was added to the list of US Open withdrawals on Wednesday, as Kei Nishikori's 2017 season came to an end.
A host of star players have been struck down by injury, with Kei Nishikori joining Novak Djokovic and Stan Wawrinka in ending his season.
Another grand slam title would move Serena Williams level with Margaret Court's record and she hopes it could come as early as next January.
David Goffin and Tomas Berdych were among five seeds to be knocked out in opening round matches at the ATP 1000 tournament in Cincinnati.
Former world number one Maria Sharapova was left with goosebumps after being given a US Open wildcard.
Karolina Pliskova's excellent record against Garbine Muguruza came to an end in Cincinnati as she was beaten 6-3 6-2.
After beating Rafael Nadal, Nick Kyrgios discussed his struggles against lesser opponents, stating: "These matches aren't the problem".
Sloane Stephens proved no match for Simona Halep as the second seed raced into the Western and Southern Open final.
Top seed Rafael Nadal ran out of steam against Nick Kyrgios in Cincinnati, where David Ferrer toppled Dominic Thiem on Friday.
For the first time in his career Grigor Dimitrov will contest an ATP 1000 Masters final after beating John Isner in Cincinnati
Nick Kyrgios was too good for David Ferrer, setting up a meeting with Grigor Dimitrov in the final in Cincinnati.
Nick Kyrgios lies in wait for Rafael Nadal after the Spaniard beat Albert Ramos Vinolas 7-6 (7-1) 6-2 in the Western and Southern Open.
Simona Halep failed to go number one in the world for a third time this year after being thrashed by Garbine Muguruza.