French Open champion Stan Wawrinka outslugged gutsy South Korean teenager Chung Hyeon 7-6 7-6 7-6 to reach the third round of the US Open.
Wawrinka belted 26 aces and hammered in 62 winners on another sweltering hot day at Flushing Meadows but the 19-year-old Chung held his own against the fifth seed, ripping 28 winners and winning 21 of 33 forays to the net.
Wawrinka, in his all-or-nothing, aggressive style, also registered 66 unforced errors against the bespectacled Korean, a 2013 Wimbledon junior finalist who is now ranked 69th.
"It was a really tough match, more than three hours," said the 30-year-old Swiss ace. "I was playing good tennis. He's a great fighter and not easy to play."
Wawrinka, who also has the 2014 Australian Open crown to his credit, next faces Belgium's Ruben Bemelmans, who advanced when American Jack Sock retired due to cramping while leading 6-4 6-4 3-6 1-2.
Meanwhile, Britain's Johanna Konta pulled off the biggest win of her career as she knocked out ninth seed Garbine Muguruza to reach the third round.