Nalbandian made light work of his fellow countryman in the opening set, but world number 65 Berlocq broke his serve three times to take the second set.
An early break in the deciding set helped the world number 19 on his way to victory, however, and Nalbandian will face Horacio Zeballos in the second round, after Zeballos beat Ricardo Hocevar 7-6(2) 6-4.
Meanwhile, second seed Juan Monaco crashed out after his 6-4 3-6 6-4 first-round defeat to Maximo Gonzalez.
World number 22 Monaco - who is 118 places higher than Gonzalez in the world rankings - has reached the quarter finals in Chile for the last three years, but was well beaten by Gonzalez, who goes on to face Joao Souza in the second round.
Souza, from Brazil, defeated Pablo Cuevas 6-4 7-5.
Colombia's Santiago Giraldo defeated Facaundo Bagnis 2-6 6-3 6-2 to book his place in the second round, where he will be joined by Rui Machado - who defeated wildcard Felipe Rios 6-2 6-0 - and Caio Zampieri - who ousted Nicolas Massu 7-6(7) 7-5.