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.
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.