American Mackenzie McDonald has beaten top seed Juan Martin del Potro in the quarter-finals of the Delray Beach Open.
McDonald, ranked world No.84, advanced to his first ATP Tour semi-final with the 6-4 3-6 7-6 (7-5)victory.
Del Potro was playing in his first event after four months out because of a right knee injury.
Steve Johnson squandered an early lead in his 1-6 6-3 7-6 (7-5) defeat to Moldavan Radu Albot.
McDonald and Albot will meet on Saturday for a place in the final.
American second seed John Isner hit 24 aces and was untroubled on serve in his 7-6 (7-2) 6-4 defeat of Frenchman Adrian Mannarino.
Isner's opponent in the last four will be British qualifier Dan Evans, who swept aside sixth-seeded Italian Andreas Seppi 6-4 6-4.
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