The seventh-seeded Bulgarian advanced to his eighth ATP World Tour Masters 1000 quarter-final with a 6-3 7-5 victory over Del Potro, who struggled with the intense heat in the closing stages of the one hour, 39-minute match.
In later matches, John Isner never dropped a service game on his way to a 7-6(4) 7-5 win over fellow American Frances Tiafoe.
Donaldson, who defeated Nikoloz Basilashvili in straight sets on Thursday, will be one of four unseeded players in the quarters following a series of upsets early in the tournament.
Third seed Dominic Thiem needed two tie-breakers to dispatch France’s Adrian Mannarino 7-6(4) 7-6(3) and set up a meeting with Spain’s David Ferrer, who upset 11th-seeded Pablo Carreno Busta 6-4 6-4.
Grigor Dimitrov beat big-hitting Argentine Juan Martin del Potro for the first time in six career attempts to book a place in the last eight at the Cincinnati Open on Thursday.
- Kyrgios fumes as rain wreaks havoc in CincinnatiYahoo7 News
- Grigor Dimitrov beats Del Potro for first time to reach Cincinnati quartersIndia Today
- Sports news roundup: Dimitrov advances in Ohio tennis tournamentAkron Beacon Journal
- Grigor Dimitrov vs Yuichi Sugita: Cincinnati Masters 2017 preview and predictionRealSport101
- Dimitrov sees off Del PotroEurosport.com
- Grigor Dimitrov claims maiden victory over Juan Martin del Potro in CincinnatiSkySports
- Grigor Dimitrov rallies past Juan Martin del Potro in OhioSports Illustrated
- Grigor Dimitrov Wins Against Juan Matin del Porto in CincinnatiNovinite.com
- Dimitrov overcomes Delpo challengeHERE. NOW