MASON, Ohio (AP) Grigor Dimitrov upset second-seeded Stan Wawrinka 6-4, 6-4 on Thursday to earn his first berth in the quarterfinals of the Western & Southern Open.
Dimitrov's fourth straight win over Wawrinka sets up a matchup with the winner of Thursday's match between Jo-Wilfried Tsonga and 2016 Olympics doubles bronze medalist Steve Johnson.
Tied 3-3 in the second set, Wawrinka committed two unforced forehand errors and Dimitrov got the break he needed to take command.
Dimitrov is the second player to reach the Cincinnati quarterfinals, joining Dominic Thiem.
In the women's draw, Karolina Pliskova became the first woman to reach the quarterfinals. Pliskova defeated Misaki Doi 7-5, 6-3. Doi was a ''lucky loser'' who replaced top-seeded Serena Williams when Williams withdrew with a shoulder injury on Monday.