Reigning champion and top seed John Isner powered past Alex de Minaur into the Atlanta Open quarter-finals.

Isner – a four-time champion of the ATP 250 tournament – made light work of talented Australian youngster De Minaur 6-3 6-2 on Wednesday.

Big-serving American Isner, who was playing for the first time since his six-hour, 36-minute-epic against Kevin Anderson in the Wimbledon semi-final – did not face a break point as he earned a last-eight showdown with seventh seed Mischa Zverev.

"It was a pretty comprehensive win," Isner said. "You never know how you're going to come out. This was my first match on hard court since Miami, so it's been a little bit and hadn't practised too much because the focus was on resting after that long match [at Wimbledon] so I'm very happy."

Zverev reached the quarters with a comprehensive 6-4 6-2 victory against Russian veteran Mikhail Youzhny.

Australian Open semi-finalist and third seed Hyeon Chung defeated Taylor Fritz 6-4 7-6 (7-5), while Ryan Harrison outlasted Lukas Lacko 2-6 6-2 6-3.