Nadal, who has won the tournament on three occasions and is the second seed this year, was in good physical form after a walkover in the second round at the Flushing Meadows here on Saturday as his opponent, Thanasi Kokkinakis, forfeited due to a shoulder injury, Efe news reports.
Chung, on the other hand, was still reeling from a tough five-set duel against Spaniard Fernando Verdasco that lasted over three hours and 20 minutes.
In Saturday's face-off, Nadal won the first set in 41 minutes.
The 23-year-old Korean player, world No. 170 in the ATP rankings, improved his play during the second set, though the Spaniard ended up snagging it as well aided by Chung's many unforced errors, which reached a total of 37 throughout the match.
Chung, who stopped playing between February and July due to a back injury, was overwhelmed in the third set by Nadal's powerful serves and surgical precision.
"When (Chung) is healthy, he showed how good he is to everyone. He's had injuries and, from my personal experience, I know how tough it is to be injured," Nadal said of his young opponent during his on-court interview.
"It's a great event for him and I wish him a healthy career. That's the most important thing."
The Spaniard added that he was attempting to try to play less but more aggressively, which is why he declined to participate in the Cincinnati Masters event.
"I'd like to play everywhere, but I'm not 25 anymore," he said.
Nadal is next set to face Croat Marin Cilic.
( With inputs from IANS )