Serena Williams returned to winning ways thanks to a 6-1 6-2 rout of Daria Gavrilova in her first-round match on Monday.
Former world number one Novak Djokovic was pushed by Steve Johnson after Andy Murray lost his first-round match on Monday.
Novak Djokovic claimed a hard-fought 6-4 7-6 (7-4) win over Steve Johnson to reach the second round in Cincinnati.
Former world number one Andy Murray is not sure if he is physically ready to challenge at grand slams following Monday's loss in Cincinnati.
Roger Federer will make his ATP return against Peter Gojowczyk on Tuesday and the 37-year-old is anxious.
A slow start proved costly for Andy Murray, who fell at the first hurdle in Cincinnati.
The honour of being the first qualifier for this year's WTA Finals goes to French Open champion Simona Halep.
Sloane Stephens has pushed Simona Halep all the way in two finals in 2018 and the Romanian believes it has made her a better player.
Kyle Edmund earned his first Cincinnati victory by defeating Mackenzie McDonald 6-3 6-2 on Sunday.
Rafael Nadal pulled out of the Cincinnati Masters just hours after claiming his 80th ATP Tour title via the Rogers Cup.