Group B leaders Deportivo Cali made it four wins from as many matches in the semi-final stage with a 1-0 victory over Once Caldas.
With two matches remaining, they are six points clear of Deportivo Pasto, but cannot be overhauled because they finished higher on the table in the first stage.
Nestor Camacho hammered in a 44th-minute penalty down the middle for the only goal of the game.
Both teams were reduced to 10 men late on as Gustavo Cuellar and Patricio Perez were red-carded.
In Group A, Atletico Nacional moved three points clear with a hard-fought 2-1 victory at home to Junior.
Kick-off was delayed several hours due to a flooded Estadio Atanasio Girardot pitch in Medellin.
When play resumed, the hosts needed just two minutes to open the scoring when former Aston Villa striker Juan Pablo Angel headed past Sebastian Viera.
Wilder Guisao appeared to have sealed it on 66 minutes and the hosts held on despite Edison Toloza's late strike.
Itagui scored twice in as many minutes in a 2-0 win at Santa Fe and Jorge Ramirez's second-half hat-trick helped Deportivo Pasto hammer Millonarios 4-1.
