Jiri Vesely was eliminated in the first round as all three seeds in action fell at the Argentina Open on Tuesday.
Czech sixth seed Vesely was ousted 6-4 6-3 by world number 85 Blaz Rola, who notched just his second ATP World Tour win of the season after one hour, 31 minutes.
Slovenian Rola won four of 12 break points throughout the clay-court contest in Buenos Aires as the 2015 Heineken Open champion failed to make it past the first hurdle in Argentina.
Next up for Rola is a second-round showdown with local qualifier Facundo Bagnis, who saw off Marco Cecchinato 4-6 7-5 6-3.
Pablo Andujar and Pablo Carreno Busta were also sent packing in the Argentina capital.
Andujar - the Spanish seventh seed - forced a deciding third set after winning the second but eventually lost to countryman Nicolas Almagro 6-3 3-6 6-2.
Serving was Andujar's biggest problem, with his first (60 per cent) and second serve success rates (47 per cent) well below that of Almagro, who won 76 per cent of his first service points and 71 of his second.
Almagro's triumph earned him a meeting with compatriot Albert Ramos-Vinolas following the Spaniard's 6-4 6-1 win over Horacio Zeballos.
Illness cost Carreno Busta a spot in the second round after the eighth-seeded Spaniard was forced to retire when trailing Federico Delbonis 7-6 (7-2) 3-0.
Delbonis will face Paolo Lorenzo in the next round.
There was another upset on Tuesday as world number 186 and local qualifier Renzo Olivo dispatched Jarkko Nieminen 7-6 (7-3) 5-7 6-0.
Olivo's surprise victory set-up a clash with second seed Tommy Robredo.
Meanwhile, Facundo Arguello, Carlos Berlocq and Guido Andreozzi advanced.
Arguello accounted for Albert Montanes 6-3 6-2, Berlocq prevailed 6-3 6-3 against Diego Schwartzman and Andreozzi made light work of Andres Molteni 6-2 6-2.