The seeds tumbled in the first round of the Brasil Open on Tuesday as Albert Ramos, Paolo Lorenzi, Nicolas Almagro and Pablo Andujar all bowed out.
Ramos was the highest-ranked casualty to be dumped out in Sao Paulo, but there was no sign of things to come when he whitewashed Pablo Carreno-Busta in the opening set.
However, his fellow Spaniard fought back brilliantly to claim a 0-6 6-4 7-6 (7-2) victory over the fifth in a match lasting two hours and 12 minutes.
Carreno-Busta twice broke for the lead in the decider only for Ramos to hit back each time, but it proved in vain as the former dominated the tie-break.
Italian sixth seed Lorenzi - the champion in 2014 - was the overwhelming favourite against qualifier Blaz Rola with 108 places separating them in the rankings, but the underdog prevailed 7-6 (7-3) 3-6 7-6 (7-5).
Seventh seed Almagro also crashed out, eliminated by wildcard Thiago Monteiro 6-3 7-5.
Andujar, seeded eighth, raced through the first set of his contest against Gastao Elias 6-1, but after losing the second 6-4 he retired with a seeming left arm injury.
Facundo Bagnis also pulled off a mini upset in a 6-4 6-1 beating of Paul Henri-Mathieu, Dusan Lajovic was a 6-2 6-2 victor over 2015 runner-up Luca Vanni, and Inigo Cervantes defeated Spanish compatriot Marcel Granollers 6-3 6-4.
Diego Schwartzman was leading 6-4 4-2 in his contest against Horacio Zeballos when his opponent retired, while Santiago Giraldo was a 6-2 6-2 victor against Marco Cecchinato.