Junior have edged Atletico Nacional 1-0 in the first leg of their Colombia Primera A Apertura final on Sunday.
Edison Toloza s 55th-minute goal saw Julio Comesana s men to the hard-fought win at their Estadio Metropolitano Roberto Melendez home.
Junior, seven-time champions, last won a title in 2011 and need another result at Atletico Nacional s Estadio Atanasio Girardot on Wednesday to add to that crown.
The win extended Junior s unbeaten run to six matches, while Atletico s struggles continued.
Perhaps affected by their run to the Copa Libertadores quarter-finals, Atletico have lost four of their past five matches in all competitions.
It was a scrappy winning goal for Junior, with Toloza tapping in from close range after a corner went uncleared by the visitors.