A midfielder from the Universidad Católica youth system,[1] Hermosilla emigrated to El Salvador and made his professional debut with Alianza.
[3] After a stint with Municipal from Guatemala, he returned to Chile and joined Colo-Colo,[4] winning the 1970 Primera División.
[9] A historical manager of Cobreloa, he led the team in four stints, having begun his career as the assistant of Jorge Siviero in the same club in 1987.
He also coached Coquimbo Unido, Unión San Felipe, Rangers de Talca and Audax Italiano.
[1] In addition, he started the Cobreloa Academy based in Santiago, where began his career players such as Eduardo Vargas, Charles Aránguiz and Esteban Pavez.