The 36-year-old Ferrer, who has been ranked as high as number three and has won the title in Buenos Aires three times previously, showed impressive form despite his pledge to retire in May.
Now ranked 149th globally, Ferrer is playinkg the last tournaments of his career, having announced last August that he will retire from professional tennis at the next Masters-1000 event in Madrid.
"I am very happy to win, to take it forward. My stage as a tennis player is over, but I still feel competitive ... I felt somewhat awkward because I come from several weeks without competing, and I can not demand more, but in the second set I had good feelings, "said the Valencian.
A special guest in Buenos Aires, Ferrer was welcomed onto centre court by a guard of honour made up of tennis stars including Gabriela Sabatini, Guillermo Coria, Juan Monaco, Diego Schwartzman and his compatriot Marc López.