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 on Thursday.
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.