(Reuters) - 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.

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.

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.

Rain put a halt of Australian Nick Kyrgios' match against Ivo Karlovic with the Croatian leading 4-3 in the first set.