The top-seeded Monaco claimed his first title since winning three in 2007 -- and all have come on clay. The victory marked a breakthrough for the 27-year-old Monaco, who lost in the final at this tournament in 2008 and 2010.
"The third time is lucky they say, so this time it's true," he said.
It was the first ATP final for Berlocq, who advanced after defeating second-seeded Juan Ignacio Chela, another Argentine.
Monaco started well and led 4-1 before going on to win the first set. He led 4-2 in the second and seemed headed for victory before Berlocq evened the match and won the tiebreak. Monaco returned to form in the third set and broke Berlocq twice.
Berlocq, who turned 29 on Friday, dropped only one set during the week.
The Chilean tournament is the start of a month-long clay court swing across Latin America, with other events upcoming in Brazil, Argentina and Mexico.