Top seeds Daniil Medvedev and Ashleigh Barty are among the big names through to the quarter-finals in Cincinnati.
Russian world number two Medvedev beat Bulgaria’s Grigor Dimitrov 6-3 6-3.
He extends his winning streak to seven matches, having won the Canadian Open title on Sunday.
In the women’s tournament, Australia’s world number one and recent Wimbledon winner Barty stormed past Belarus’ defending champion Victoria Azarenka 6-0 6-2.
The Czech Republic’s Barbora Krejcikova beat Spain’s 2017 champion Garbine Muguruza 6-1 6-7 (5-7) 6-2, while Germany’s two-time Grand Slam champion Angelique Kerber is also through to the last eight, marking her 10th Cincinnati appearance with a 4-6 6-2 7-5 win over Latvia’s Jelena Ostapenko.
Czech 11th seed Petra Kvitova later defeated Tunisia’s Ons Jabeur 6-1 6-2.
In the men’s draw, German third seed Alexander Zverev progressed with a 6-2 6-3 win over Argentine Guido Pella, while Spain’s seventh seed Pablo Carreno Busta defeated ninth seed Hubert Hurkacz 7-6 (8-6) 7-6 (7-3) to set up a quarter-final clash with Medvedev.
Benoit Paire of France beat American John Isner 7-6 (7-1) 6-7 (2-7) 6-1, but French compatriot Gael Monfils was toppled 7-6 (7-2) 7-6 (7-5) by Russian fourth seed Andrey Rublev.
