Chung, ranked 170th, defeated American Ernesto Escobedo (206th) in five sets, 3-6, 6-4, 6-7 (5-7), 6-4, 6-2, at the US Open men's singles at Billie Jean King National Tennis Center in New York on Tuesday (local time).
By winning the 3:37 marathon affair, Chung has reached the second round at the US Open for the third consecutive year. He will take on Fernando Verdasco of Spain in the next round.
Chung, the 2018 Australian Open semifinalist, reached as high as No. 19 in the world rankings last spring but has since fallen on hard times due to assorted injuries. After playing in the second round at the Australian Open in January this year, Chung ended up missing the next two majors, the French Open and Wimbledon, with injuries. He had to play in the qualifiers to get into the US Open.
Chung, who returned to action late last month, struggled early on against Escobedo, dropping the opening set 3-6 against the wild-card entry.
Chung trailed 2-4 in the second set before winning the next four games to win the set and even the match.
Escobedo won the third set in a tiebreak, fending off Chung who was once down 2-5 and cut it to 5-6.
Tied at 4-4 in the fourth set, Chung broke Escobedo and then held his own serve to force a 2-2 tie in sets.
In the deciding fifth set, Escobedo double-faulted twice to get broken in the first game, as Chung charged out ahead to a 4-0 lead en route to a grinding victory.
Chung had 65 winners against Escobedo's 46.
Verdasco is a former top-10 player who beat Chung in their only previous meeting in 2015 at a clay court event by 7-6 (7-5), 6-2.
The winner of this second round match will be on collision course with world No. 2 Rafael Nadal, a three-time US Open champion. (Yonhap)