Mason - Grigor Dimitrov rallied from 4-1 second-set deficit for a 6-3, 7-5 win over Juan Martin del Potro and reached the Western & Southern Open quarter-finals on Thursday.
The seventh-seeded Dimitrov advanced with his first career win in six matches against Del Potro. Dimitrov improved to 15-13 in his last 28 matches after opening the season 16-1.
Second-seeded Simona Halep became the tournament's first quarterfinalist with a 6-4, 6-3 win over 15th-seeded Anastasija Sevastova.
It's the fifth straight year Halep, No. 2 in the rankings, has at least reached the W&S quarterfinals. She was runner-up to Serena Williams in 2015.
Svetlana Kuznetsova advanced with a 6-2, 6-4 win over Carla Suarez Navarro.