James Duckworth and Rinky Hijikata were both successful at the ATP 250 event in North Carolina on Tuesday (Wednesday AEST), but compatriots Cruz Hewitt and Adam Walton were eliminated.
With the US Open getting underway in New York next week, world No.79 Duckworth, still searching for his first tour title, triumphed 6-3 7-6 (7-5) over Argentine sixth seed Mariano Navone in a huge confidence boost.
The 34-year-old Sydneysider was broken when trying to serve out the opening set at 5-2, before getting it done against the 48th-ranked Navone in 37 minutes.
Duckworth fell behind 3-0 in the second set but fought back to win the tiebreaker and set up a clash against Lorenzo Sonego, after the Italian downed ninth seed Adrian Mannarino of France, 6-1 7-6 (7-5).
Hijikata's clash went the distance, overcoming Belgian fifth-seed Raphael Collignon 3-6 7-6 (9-7) 7-6 (7-5) in a three-hour 11-minute epic.
The 25-year-old world No.85 dropped serve in the eighth game to lose the first stanza. Both players struggled on serve in sets two and three, broken a total of 10 times between them, before Hijikata - also title-less on tour - booked a match-up with Benjamin Bonzi of France.
Wildcard Cruz Hewitt, the 17-year-old son of former world No.1 Lleyton Hewitt, suffered a 6-1 7-5 loss to Britain's top player and fourth seed Arthur Fery.
Earlier, Adam Walton was beaten 6-2 5-7 6-3 by third-seeded Peruvian Ignacio Buse.
Elsewhere, 22-year-old American Martim Damm stunned top-seeded Russian and current world No.8 Daniil Medvedev 7-5 6-3 in 82 minutes, while second seed Luciano Darderi won the all-Italian clash with Mattia Bellucci 2-6 6-4 6-2.
There were also wins for eighth-seeded Juan Manuel Cerundolo, his 10th-seeded fellow Argentine Sebastian Baez and Dutch 13th seed Botic Van De Zandschulp.
But the 11th and 12th seeds, French pair Luca van Assche and Quentin Halys, are out.
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