Cali top Group B with three points after they arrested two deficits at the Estadio Olimpico Pascual Guerrero, eventually clinching the ascendancy in the 86th minute when Harrison Mojica curled in a left-footed attempt from the edge of the area.
Earlier, a Mauricio Mina header in the ninth minute had visitors Pasto ahead, only for Carlos Lizarazo to lash home a shot from just outside the area after controlling the ball with his chest.
Pasto hit the front once more with a sensational long-range strike from Juan Villota on 57 minutes, only for Sergio Romero to hit back on the hour-mark - finishing off some impressive lead-up play from Cali to tuck away past on-rushing Pasto goalkeeper Lucero Alvarez.
Then Mojica put Cali in front for the first time in the match with a sublime effort from the right side of the area, with his curling effort worthy of the winner.
It was the ideal start for Cali to the six-match phase, while Pasto already have an uphill battle to try and top the group to advance to the Clausura final.
The early leader in Group A is Junior, after they beat Itagui 1-0 away from home.
Edwin Cardona tucked away the game's only goal on 33 minutes, before referee Hernando Buitrago had the biggest influence of the second half - as he sent off Itagui's John Restrepo and Carlos Arboleda.
Nine-man Itagui were then given a minor lifeline, as Junior substitute Edison Toloza - who replaced goalscorer Cardona on 69 minutes - lasted just eight minutes before he saw red to make it 10 against nine.
But Junior still held on to go top of the group with the valuable points on the road.
