Bernard Tomic got his season going with a first-round win at the New York Open, while Tennys Sandgren made an early exit.
Tomic, who suffered a first-round loss at the Australian Open, brushed past Lukas Lacko 6-4 6-2 in his opener at the ATP 250 event.
The Australian served nine aces in a 54-minute victory – his first of the year – and next faces top seed John Isner.
Sandgren, the eighth seed, was edged by Paolo Lorenzi 7-6 (7-4) 6-7 (4-7) 6-4, while Jordan Thompson got through, beating Noah Rubin 6-7 (7-9) 7-5 6-1.
At the Argentina Open, the only seed in action departed, Nicolas Jarry going down to qualifier Lorenzo Sonego 6-7 (3-7) 6-4 6-3.
Albert Ramos-Vinolas was too good for qualifier Rogerio Dutra Silva 6-3 6-4, Maximilian Marterer eased past Facundo Bagnis 6-4 6-2 and Christian Garin overcame Felix Auger-Aliassime 3-6 7-5 6-3.