Sock, Chung through at Delray Beach
Defending champion Jack Sock reached the Delray Beach Open second round, while Hyeon Chung also advanced on Monday.
Sock broke once in each set on his way to a 6-4 6-4 victory over Australian qualifier John-Patrick Smith.
The American top seed only created two break points - converting both - while saving four to get through his opener.
In action for the first time since his run to the Australian Open semi-finals, Chung - the eighth seed - got past lucky loser Cameron Norrie 3-6 6-3 6-1.
Meanwhile, Donald Young crushed Ramkumar Ramanathan 6-1 6-2 and Frances Tiafoe overcame Matthew Ebden 6-2 2-6 6-2.