Top seed John Isner survived a scare as Christian Harrison came desperately close to causing another shock at BB&T Atlanta Open.
Harrison beat Alejandro Falla on his ATP Tour singles debut on Wednesday and the 19-year-old put up a brave fight against Isner in the second round.
Isner dug deep, though, to clinch a 7-6 (11/9) 4-6 7-5 victory to prevent Harrison joining his older brother Ryan in the quarter-final.
The 21-year-old caused an upset of his own by ousting fourth seed Igor Sijsling 6-4 6-3.
Harrison's reward is a last-eight clash with Santiago Giraldo - who overcame Michael Russell after he retired when trailing 5-7 6-3 3-0 - while James Blake will take on Isner following his 6-3 6-2 victory over eighth seed Evgeny Donskoy.
Second seed Kevin Anderson was pushed all the way but came through 6-7 (7/9) 6-2 6-2 against Matthew Ebden and will face Denis Istomin next after the Uzbekistan player defeated fifth seed Lu Yen-hsun 7-5 6-2.
Former Wimbledon doubles champion Jonny Marray and fellow Briton Colin Fleming have reached the semi-finals in Atlanta.
Marray and Fleming beat the American pair of James Black and Jack Sock 6-3 6-2 in their quarter-final, setting up a last-four clash against Lleyton Hewitt and Chris Guccione.