Clavet, who has indicated that he intends to retire soon, was handed a 6-4, 4-6, 6-1 first-round loss by Mello at the same tournament he won in 1997.
"I've always felt at home here," Clavet said. "Undoubtedly, this is one of my favorite tournaments. I've always been treated like family here, and I appreciate that very much."
Another qualifier, Ivan Miranda of Peru, outlasted Andre Sa of Brazil, 7-5, 3-6, 7-6 (7-1); Mariano Zabaleta of Argentina routed qualifier Filippo Volandri of Italy, 6-1, 6-2; and David Ferrer dispatched fellow Spaniard Albert Portas, 6-1, 6-4.
"I played well in the first set, but in the second set, I gave Portas a chance to come back," Ferrer said.
Patricia Wartusch of Austria pulled off the only upset on the women's side, rallying for a 3-6, 6-4, 6-3 victory over sixth-seeded Tina Pisnik of Slovenia.
Also winning were Cristina Torrens Valero of Spain, Klara Koukalova of the Czech Republic, and Shinobu Asagoe of Japan.
The men's winner receives $52,000, while the women's champion receives $27,000.