Jaime Valdes netted a 72nd-minute winner for Colo Colo, who recorded a 2-1 victory at Universidad Catolica on Sunday.
With Universidad Chile held a day earlier, Hector Tapia's men climbed top of the table thanks to their superior goal difference with both sides level on 38 points.
It is set to make for a thrilling finish to the Apertura campaign with two matches remaining.
Colo Colo went ahead on Sunday thanks to an own goal, with Cristian Alvarez scoring past his own goalkeeper Franco Costanzo.
Mark Gonzalez levelled for the hosts in the 57th minute, but Valdes would prove to be the hero with his goal a quarter of an hour later.
A day earlier, Universidad Chile gave up a lead to draw 1-1 at home to Barnechea.
Patricio Rubio opened the scoring eight minutes before half-time following a goalmouth scramble.
But Oscar Hernandez drew the visitors level seven minutes after the break as his free-kick took a huge deflection before going in off the post.
Santiago Wanderers are just a point behind the top two after recording a 2-1 win over Nublense.
Roberto Gutierrez and Jorge Luna were on the scoresheet, the latter from the penalty spot, to put Wanderers ahead.
Sebastian Varas scored a spot-kick for the visitors, who were unable to find an equaliser and had Boris Sagredo sent off.
Saturday's clash between San Marcos and Deportes Iquique was suspended in the 71st minute.
San Marcos' Venezuelan forward Emilio Renteria scored before racist chanting directed towards him led to the game being halted.
Antofagasta overcame Cobreloa 2-1 and Union Espanola claimed a 3-1 victory at Huachipato.
Renato Ramos' brace helped Palestino to a 3-2 win over Union La Calera, Cobresal beat O'Higgins 3-1 as both teams finished with 10 men and Audax Italiano crushed Universidad Concepcion 4-1.