Sam Groth suffered another first-round exit after losing to Illya Marchenko in straight sets at the Memphis Open on Monday.
Groth headed to the United States, having fallen at the first hurdle of the Brisbane and Sydney internationals, prior to reaching the Australian Open second round last month.
But the big-serving Australian sixth seed was eliminated early again, this time at the ATP 250 tournament in Memphis, as Marchenko triumphed 7-6 (7-4) 7-6 (7-2).
Groth, who was never broken during the one hour, 53 minutes contest, saved two match points in the second set but he could not deny the Ukrainian.
Marchenko will play Yoshihito Nishioka in the second round following the Japanese qualifier's 6-3 6-4 victory against Jared Donaldson.
The only other seed in action on Monday, Denis Kudla, safely navigated his way into the second round after downing Rajeev Ram in an all-American contest.
Kudla - seeded fifth - accounted for Ram 6-4 6-2.
Next up for Kudla is Kazakh Mikhail Kukushkin, who eased past Luca Vanni 6-4 7-6 (7-4).
In Monday's final match, Ryan Harrison prevailed 6-7 (0-7) 7-6 (10-8) 6-4 against Frances Tiafoe.