Atlanta - Reilly Opelka saved two match points en route to upsetting third seed Kevin Anderson 6-7 (5/7), 6-3, 7-5 and advancing to the quarter-finals of the ATP Tour's Atlanta Open.
The 2.11 metre tall Opelka, who is ranked 556th in the world, registered his first win over a top 30 ATP opponent.
The 18-year-old American twice faced match point with the hard-serving South African serving at 5-4 in the third set. He got out of trouble both times and went on to win the final three games of the match.
Opelka blasted 20 aces and had six double faults against the 28th-ranked Anderson, who finished with 14 aces and 14 double faults.
Opelka received a wild-card entry into the Atlanta tournament. The 2015 Wimbledon junior champion next faces seventh-seeded Donald Young, who rallied to beat Tim Smyczek 4-6, 7-6 (7/1), 6-3.
Young trailed 3-0 in the second set before seizing control. Top-seeded John Isner cruised into the quarter-finals with a 6-4, 6-0 rout of France's Adrian Mannarino.
Results from the ATP event in Atlanta on Wednesday (x denotes seeding):
Reilly Opelka (USA) bt Kevin Anderson (RSA x3) 6-7 (5/7), 6-3, 7-5
John Isner (USA x1) bt Adrian Mannarino (FRA) 6-4, 6-0
Donald Young (USA x7) bt Tim Smyczek (USA) 4-6, 7-6 (7/1), 6-3