A stoppage-time penalty from Esteban Paredes saw Colo Colo edge past Cobresal, as Santiago Wanderers also extended its winning run.
Third-placed Wanderers made it six wins in a row in the Chilean Primera Division to keep the pressure on leader Universidad de Chile, while Colo Colo remains second after its fourth consecutive victory.
But Hector Tapia's side had to do it the hard way at Cobresal's Estadio El Cobre with Paredes converting from the spot, after Rodrigo Urena had dragged down Felipe Flores in the box as the Colo Colo man attempted to get his head to a cross from the left.
Before Paredes could take the penalty, however, Cobresal delayed proceedings for five minutes due to its protests with unused substitute Fabian Cerda shown a red card after disputing the referee's decision from behind the home side's goal, while Rodrigo Urena was also sent off.
Deportes Iquique and Nublense played out a 1-1 draw, while Agustin Gonzalez struck in the second half for Union La Calera to secure a 2-2 stalemate at Audax Italiano.
Colo Colo's win took it to 32 points, two adrift of Universidad de Chile, which won the Clasico Universitario 3-0 over Universidad Catolica.
Patricio Rubio struck in the third minute and with three minutes remaining in the derby in Santiago de Chile, while Matias Corujo scored Universidad de Chile's second goal in the first half.
Santiago Wanderers (31 points), unbeaten in the Chilean top tier since August, needed a penalty to defeat O'Higgins 1-0 with Jorge Luna scoring from the spot in the 67th minute.
Promoted club Barnechea continued its surge up the table with a 1-0 win over Union Espanola, making it four games without a loss, while Palestino trumped Antofagasta 3-1.
Huachipato won 2-0 against Cobreloa and San Marcos played out a scoreless draw with Universidad de Concepcion.