Top seed Dimitrov retires in his opening match at the Winston Salem Open

Top overall seed at the Winston Salem Open, Grigor Dimitrov, won the first set of his opening match against Dominic Thiem 6-0 before being forced to retire due to illness symptoms while trailing 4-2 in the second.

The first set was total domination from the Bulgarian, winning 80 per cent (12-of-15) of the points against Thiem's serve as he breezed through the opening frame in 25 minutes, but after experiencing dizziness and shortness of breath in the second set, he decided to pull the plug on his match after a visit from the doctor.

Thiem will play England's Jack Draper in the next round after he was too strong down the stretch for Italy's Fabio Fognini, winning 6-2 4-6 6-1.

Meanwhile, it was relatively smoother sailing for second second Botic van de Zandschulp in his all-Dutch matchup against Tallon Griekspoor, converting both of his two break point opportunities to win 7-6 (7-5) 6-3.

Earlier in the day, in-form Belarusian and 11th seed Ilya Ivashka used his powerful serve to overwhelm Germany's Peter Gojowczyk 6-4 6-2.

Ivashka will meet Switzerland's Marc-Andrea Huesler next after the world number 102 passed a stiff test against Sweden's Mikael Ymer, with his 6-4 6-4 win likely elevating him into the top-100 when the next rankings are released.

Richard Gasquet at 36 years young upset 20-year-old Italian Lorenzo Musetti 7-6 (7-5) 4-6 6-1, and he will play Steve Johnson next after the big American defeated Spain's Pedro Martinez 7-6 (7-2) 6-2.

Serbia's Laslo Djere needed almost three hours to get the better of Portugal's Joao Sousa 4-6 6-3 7-6 (7-5), and Djere will play Australia's Jason Kubler after he handled South Korea's Kwon Soon-woo 7-5 6-2.

The other two Aussies in action were less successful, as John Millman fell 6-4 6-4 to Spain's Albert Ramos-Vinolas, and James Duckworth went down 6-3 6-3 against Maxime Cressy.

Finland's rising star Emil Ruusuvuori was disappointing in his 6-4 6-1 loss to France's Adrian Mannarino, and fellow Frenchman Benjamin Bonzi also got the job done against England's Kyle Edmund 6-4 7-6 (7-5).

In the late session, 15th seed Jaume Munar defeated Tseng Chun-hsin 6-3 6-4, and in the last match of the night, Lorenzo Sonego beat Alejandro Tabilo 7-5 6-1.