DELRAY BEACH, Fla. — American Mackenzie McDonald beat No. 1-seeded Juan Martin del Potro on Friday night in the quarterfinals of the Delray Beach Open, 6-4, 3-6, 7-6 (5).
McDonald, ranked 84th, advanced to his first ATP Tour semifinal. Del Potro was playing in his first event after missing four months because of a right knee injury.
No. 4 Steve Johnson of the United States squandered an early lead and lost to Radu Albot 1-6, 6-3, 7-6 (5). Albot will play McDonald on Saturday.
No. 2 John Isner hit 24 aces and won every service game to beat Adrian Mannarino 7-6 (2), 6-4. Isner improved his career record against the Frenchman to 7-1.
Isner’s opponent in the semifinals will be qualifier Daniel Evans, ranked 148th, who swept No. 6 Andreas Seppi 6-4, 6-4.