The Argentinian scored the opening goal in Mushuc's 2-0 win over Universidad Catolica after just 14 minutes to take his tally in the league to nine this term.
Barreiro has three goals from his last four outings and, with Rommel Zura adding a second shortly after the half-hour mark, the hosts picked up their first win since August at the Estadio del Mushuc Runa Sporting Club.
That moved Mushuc up to second and kept them seven points behind Barcelona, who ran out 4-2 winners over bottom side Manta.
Christian Suarez scored twice while Jose Perlaza and Ismael Blanco were also on target, as goals from Efren Mera and Jose Flecha provied insufficient for the home side to grab a point.
Manta are yet to pick up a win this term, while Barcelona appear firmly on course for a 15th top-flight title.
El Nacional and LDU Quito, the sides in third and fourth, lost ground on the leaders as they played out a goalless draw at the Estadio Olimpico Atahualpa.
First-half goals from Junior Sornoza and Jonathan Gonzalez wrapped up the points for Independiente del Valle at home against Deportivo Quito.
The hosts had been held to draws in their previous two games but a dominant display before the break set up an important 2-0 win.
Olmedo showed their battling qualities at the Estadio Olimpico de Riobamba - twice coming from behind to salvage a 2-2 draw against Deportivo Cuenca.
Cristian Palacios cancelled out Silvio Gutierrez's early opener, but Hugo Bargas looked to have wrapped up maximum points for the visitors.
However, Alvaro Navarro levelled eight minutes from time and Olmedo's wait for a win in the league this term goes on.
