He was part of the midfield that conquered a string of championships under coach Ángel Labruna between 1975 and 1981, the others being Juan José López and Norberto Alonso.

[citation needed] Among them were Ramiro Pérez, Chamaco Rodríguez, Della Savia, Cierra, Carranza, Pitarch, de los Santos, and Américo Gallego, who ultimately earned Merlo's position.

In 1999, Merlo commanded Atlético Nacional of Colombia during the first half of the season; albeit successful, his managerial choices proved unpopular, and he resigned from his position.

[3] When Carlos Bilardo left Estudiantes in 2004, Merlo was offered the post of coach; the team advanced from relegation danger to the top positions, being a contender both in the 2004 Apertura and the 2005 Clausura.

[5][6] In 2009, he became the manager of Rosario Central but left the club on 15 April 2009 after only five games in charge (won three, tied one and lost one) because of personal problems with the player Ezequiel González.