Dimitrov got off to a great start by opening up a 3-0 lead against Del Potro.
The 20-year-old world No 60, a wildcard recipient, secured a 6-4 7-6 (4) victory in one hour and 36 minutes and awaits the victor of the all-American clash between Frances Tiafoe, who shocked Alexander Zverev on Wednesday, and 14th seed John Isner.
"I saw he was a bit exhausted, but he was still competing".
On his way to the quarterfinals of the Cincinnati Open, Bulgarian tennis player Grigor Dimitrov beat Argentinean Juan Martin del Porto with 6:3, 7:5 for the first time in his career, reported BGNES.
"He's a tricky opponent. a super-experienced player", said Dimitrov.
Seventh seeded Dimitrov proved in fine form against the Rio 2016 Olympic silver medallist from Argentina as he claimed the first set of the match 6-3. I knew if I keep the ball low on his backhand side and just kind of work my way into the court, it would have been the right thing to do.
One feared killed as IPOB clashes with army, police
IPOB members were said to have defied the heavy presence of security personnel and began parading the streets singing and waving Biafra flags.
Wildcard Jared Donaldson is into the quarter-finals after seeing off Nikoloz Basilashvili 6-4 7-6 (7/4), while Yuichi Sugita rallied for a 6-7 (0/7) 6-3 6-3 win over Karen Khachanov. "It's a big thing, and I'm really happy about it".
Del Potro, who on Tuesday upset 10th-seeded Czech Tomas Berdych, also saved five break points at 3-3 in the second set and clinched his 18th victory of the year on his fourth match point.
Before the rain, the Romanian Simona Halep, second seeded, was the first to qualify for the quarter-finals thanks to a victory of 6-4, 6-3 in the face of the Latvian Anastasija Sevastova, ranked 15th.
Muguruza will now face Svetlana Kuznetsova, with the Russian having cruised past Spain's Carla Suárez Navarro by a 6-2, 6-4 scoreline.
The winners will play twice on Friday as the quarter finals will take place today.
Next up for Thiem after his two-hour battle is Spanish veteran David Ferrer, who defeated compatriot Pablo Carreno Busta 6-4 6-4.
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