Hyeon Chung beat Cameron Norrie at the Delray Beach Open as he made a winning return in his first match since reaching the Australian Open semi-finals.
The 21-year-old South Korean was forced to come from behind before progressing though, eventually seeing off the lucky loser 3-6 6-3 6-1.
"It was a really tough match because the wind was really strong," Chung said afterwards. "However, I tried to stay calm. The guy played really well at the baseline so I was just trying to focus at every point.
"I am trying to enjoy it all the time, because it is my second time in Delray Beach. I am already better than last year."
Chung will face the winner of the match between Alexander Bublik and Franko Skugor in the next round.
Meanwhile, defending champion Jack Sock beat the Australian qualifier John-Patrick Smith 6-4 6-4 - his first victory of the year following his early exits at the ASB Classic and Australian Open.
"He's very unorthodox, lefty, serve and volleys a lot. Very unorthodox shots: flat, some spin, some flat, slice. Rushes the net a lot, tricky conditions, tricky player, so I'm happy to get through, definitely," Sock said afterwards.
Elsewhere, Donald Young easily defeated Ramkumar Ramanathan 6-1 6-2 while Frances Tiafoe edged a tight contest against Matthew Ebden 6-2 2-6 6-2.
Chung is 9/1 to win the Delray Beach Open, while Young can be backed at 1000/1, Sam Querrey at 1000/1 and Sock at 1000/1.
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