Seeds Fernando Verdasco and Martin Klizan were sent packing in the Brasil Open second round on Thursday.
Verdasco, the Spanish seventh seed, went down to Dusan Lajovic 6-7 (6-8) 6-3 6-4 on the clay courts in Sao Paulo.
Lajovic held every one of his service games on his way to the quarter-finals of the ATP 250 event.
Verdasco squandered three break points in the fourth game of the first set before the left-hander battled through the tie-break.
Lajovic held a set point at 6-5 up, but Verdasco won the next three points.
A break in the fourth game of the second set saw Lajovic back into the contest, which he levelled.
Verdasco and Lajovic both wasted break points midway through the deciding set, but the latter broke to 30 in the ninth game on his way to a surprise win.
The Serbian will next face Luca Vanni after the Italian won a battle between two qualifiers, beating Dutchman Thiemo de Bakker 7-6 (7-5) 3-6 6-3.
Klizan was also beaten, the Slovakian going down to Brazilian wildcard Joao Souza 3-6 6-3 6-2.
Souza will meet Argentine fourth seed Leonardo Mayer in the quarter-finals.
There was better news for two other seeds on Thursday, although Fabio Fognini and Santiago Giraldo were both pushed.
It was a much-needed win for third seed Fognini, who beat Diego Schwartzman 6-3 1-6 6-2.
The Italian had battled for form early in the season, with this win marking his first of 2015.
The sixth-seeded Giraldo overcame Argentina's Carlos Berlocq 4-6 7-5 6-3 to set up a meeting with Fognini.