Former US collegiate champion Steve Johnson caused an upset at the Winston-Salem Open as he beat second seed Andreas Seppi.
The 23-year-old recovered from losing the opening set to register a 6-7 (5-7) 6-4 7-5 victory over the Italian.
"Definitely played really well today," said Johnson, who will now face Lu Yen-Hsun.
"Felt like everything I've been working on for the last four, five, six months kind of came together, so it's nice to see the hard work pay off in big situations."
Benoit Paire, Fernando Verdasco and Juan Monaco survived scares to avoid joining Seppi in crashing out.
Fifth-seeded Paire ousted James Blake 7-6 (11-9) 2-6 6-3, No 7 seed Verdasco overcame Tim Smyczek 3-6 6-3 6-3 and Monaco, ranked eighth, secured a 6-7 (7-4) 6-3 6-4 win over Nicolas Mahut.
No 13 seed Dmitry Tursunov, Alexandr Dolgopolov and Tommy Robredo also needed three sets to progress.
Tursunov edged out David Goffin 4-6 7-5 6-1, 10th seed Dolgopolov eventually saw off Daniel Gimeno-Traver 4-6 6-1 6-4 and the No 4-ranked Robredo outlasted Guillaume Rufin 7-6 (7-5) 4-6 6-3.
Jarkko Nieminen, 11th seed, and No 9-ranked Jurgen Melzer saw their opponents pull out.
Nieminen was leading 7-5 6-7 (7-3) 3-2 when illness ended Mardy Fish's challenge, while Melzer was 7-5 6-7 (7-4) 4-2 ahead when Thiemo de Bakker retired.
Gael Monfils, the 15th seed, needed just 53 minutes to topple Guido Pella 6-2 6-2, however Roberto Bautista shocked No 14-ranked Martin Klizan 6-4 6-1.
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