Australian Matthew Ebden has been beaten by American wildcard Francis Tiafoe in the opening round of the Delray Beach Open in Florida.
Ebden lost to the 20-year-old local on Monday night 6-2 2-6 6-2.
Top-seeded Jack Sock meanwhile won his first match of the year, beating qualifier John-Patrick Smith in straight sets 6-4 6-4.
Sock, the highest-ranked American at No. 8, is attempting to become the first player to win consecutive titles at Delray since the tournament moved from Coral Springs, Florida, in 1999.
The match was his first since losing to Yuichi Sugita last month in the first round of the Australian Open. He also dropped a first-round match in Auckland, New Zealand.
Sock made it a first-day sweep for Americans. Donald Young also beat qualifier Ramkumar Ramanathan 6-1 6-2.