Ivo Karlovic suffered a surprise loss at the Memphis Open as David Ferrer and Pablo Cuevas made early exits in Buenos Aires.
Karlovic, the big-serving top seed and 2014 runner-up, was beaten 7-6 (7-2) 6-3 by Nikoloz Basilashvili in the second round at the ATP 250 event.
The Croatian managed to win just nine points against the Basilashvili serve as he bowed out on the hard-courts.
Fourth seed Steve Johnson fared much better, getting past qualifier Tim Smyczek 3-6 6-4 6-2 in an all-American clash.
Mikhail Kukushkin thrashed Darian King 6-3 6-0 and Matthew Ebden upset last year's runner-up Taylor Fritz 6-4 4-6 6-3.
At the Argentina Open, two seeds departed in the second round on the clay courts.
Three-time champion Ferrer was no match for local hope and wildcard Carlos Berlocq as he went down 6-4 6-2, while Cuevas lost to Alexandr Dolgopolov 6-3 7-6 (7-4).
The exits have opened up the draw at the ATP 250 tournament.
Gerald Melzer advanced to the quarter-finals with a 7-6 (7-4) 6-3 win over Guido Andreozzi.
Brazilian Thiago Monteiro continued his run with a surprise 6-3 6-4 victory against 2009 winner Tommy Robredo.