Lucas Barrios was the hero for Colo Colo as the Caciques claimed a 2-0 win over arch-rivals and Clausura leaders Universidad de Chile on Sunday.
Marcelo Barticciotto's side secured the win despite playing with just 10 men for the last 30 minutes after Luis Mena was sent off.
Barrios opened the scoring in the 35th minute and then added another in the 75th minute after receiving the ball from Jose Domingo Salcedo, moving past three defenders before sending a shot past Universidad goalkeeper Miguel Pinto.
Universidad de Chile had the chance to reduce the deficit but Colo Colo goalkeeper Cristian Munoz saved a penalty from former Lazio striker Marcelo Salas with seven minutes remaining.
Despite the defeat, Universidad de Chile remain on top with 29 points in Group A.
Colo Colo coach Barticciotto said: "It was a difficult match throughout. We shouldn't forget we played the leaders, a team with excellent players. This is an important victory because the title is our goal."
Barrios added: "We proved we know how to play in crucial matches. We proved we are good enough and we can get even better."