Kevin Anderson's challenge at the Winston-Salem Open ended in disappointment as the second seed was ousted by Sam Querrey in straight sets.
Querrey, who has made the semi-finals on his last two appearances at the event, rattled off a 7-6 (7-4) 6-4 victory – with Anderson struggling against the American’s dominant serve.
“I played great out there,” Querrey told atpworldtour.com. "That was the best I’ve played all summer.
"I was aggressive the whole time and returned well. I thought everything went pretty well.”
Querrey’s reward is a quarter-final clash with Guillermo Garcia-Lopez after the fifth seed from Spain recovered from a set down to beat Donald Yong 6-7 (7-4) 6-3 7-6 (8-6).
John Isner remains unbeaten at Wake Forest University, with the top seed brushing aside Mikhail Kukushkin 6-1 7-6 (7-3) to record his 12th straight win.
Next up for the two-time champion is seventh seed Lukas Rosol, a 1-6 6-2 6-2 winner over Pablo Andujar.
There were minor upsets as 12th seed Edouard Roger-Vasselin and No 15-ranked Jarkko Nieminen both bowed out. Roger-Vasselin lost 4-6 6-3 6-4 to Jerzy Janowicz, while David Goffin edged out Nieminen 6-4 4-6 6-4.
Ninth seed Yen-Hsun Lu made light of the rankings as he routed eighth-ranked Marcel Granollers 6-1 6-2, while No 14 seed Andreas Seppi ended the challenge of Nicolas Mahut 6-4 7-6 (9-7).