American Sebastian Korda, the No 4 seed, advanced to the last eight of the Citi Open when Australian Thanasi Kokkinakis retired at the William H.G. FitzGerald Tennis Center in Washington.
Korda, ranked No 22, led 6-7 (1), 7-5, 3-2 when Kokkinakis, ranked No 91, pulled out at the William H.G. FitzGerald Tennis Center in Washington on Thursday evening.
The American will play Australian Jordan Thompson, the No 7 seed, next.
Sebastian Korda defeated Chilean Cristian Garin (6-3, 6-2) ahead of his victory.
In the previous rounds of the Washington D.C. tournament, the Australian won against Max Purcell (6-7 (4), 6-4, 6-3) and No 14 seed Aleksandar Vukic (6-4, 7-6 (4)).
Washington ATP 500, other last-16 results (William H.G. FitzGerald Tennis Center, hard, USD 2.100.230, most recent results first):