A 1-0 triumph in the opening leg last week has the Chileans in position to make the last eight of this competition for the first time since 2018.
Match preview
Junior failed to get anything going throughout the opening match of this tie, registering just one effort on target last week.
It was their first defeat at the Libertadores this year, and they have now failed to find the back of the net in consecutive matches at this tournament.
Arturo Reyes saw his side drop four points when scoring first in the opening phase of this competition, including a 1-1 draw at home versus LDU Quito on matchday three.
Atletico Junior have yet to win a Libertadores fixture at home this season, playing to three consecutive draws in the opening phase.
That said, Junior are unbeaten in five successive competitive home fixtures, defeating Fortaleza in the Colombian top-flight this weekend by a score of 2-1.
Los Tiburones have not advanced from a Libertadores knockout fixture when failing to win the opening leg since 1996 when they defeated Cerro Porteno 1-0 after that first match ended 0-0.
Another resolute defensive performance from Colo-Colo in leg one of this tie has them within reach of a place in the quarter-finals.
Eterno Campeon are on a 10-match unbeaten run in all competitions, failing to concede in their last three outings.
This past weekend, their 2-0 victory over Coquimbo in the Chilean top-flight extended their winning run at home to six matches across all competitions.
Colo-Colo have failed to win their last three second-leg fixtures at the Libertadores and have not won a return engagement in the knockout portion of this tournament since defeating Club America 2-1 at this stage in 2007, but losing that tie 4-2 on aggregate.
So far at this tournament, Jorge Almiron's men have never lost when scoring first but have also never won when conceding the opener.
Meanwhile, they have never won a Libertadores away match versus Colombian opposition, but Los Albos claimed a 1-1 draw in their only prior visit to Barranquilla in 1994, losing that tie on penalties.
Atletico Junior Copa Libertadores form:
D
D
D
W
D
L
Atletico Junior form (all competitions):
Colo-Colo Copa Libertadores form:
L
D
L
D
D
W
Colo-Colo form (all competitions):
Team News
From their matchday six draw with Botafogo (0-0) to the opening game of this tie, there were three new faces in the Junior starting 11, including Jermein Pena, Andres Colorado and Yimmi Chara.
Carlos Bacca and Luis Gonzalez found the back of the net in their domestic home fixture this weekend, enabling them to earn a victory over Fortaleza.
For this decisive fixture, Colo-Colo are likely to be without Alan Saldivia, who suffered a meniscus tear earlier this month, while Cesar Fuentes is out long-term with a cruciate ligament tear.
Vicente Pizarro had the only goal in the opening leg, as Brayan Cortes collected his third clean sheet of the competition this year.
Atletico Junior possible starting lineup:
Mele; Herrera, Olivera, Pena, Fuentes; Moreno, Quintero; Castrillon, Hinojosa, Chara; Bacca
Colo-Colo possible starting lineup:
Cortes; Isla, Amor, Falcon, Wiemberg; Palacios, Pavez, Pizarro; Paiva; Correa, Cepeda
We say: Atletico Junior 1-1 Colo-Colo (Colo-Colo advances 2-1 on aggregate)
Throughout this tournament, the Colombians have been narrowly squeaking by, and we do not see them doing enough to defeat a side as disciplined defensively as Colo-Colo.