The two teams played to a one all draw in the first leg, but it is K'Ogalo, who have been grinding results that have seen the team rise to the top of the league with 40 points.
The mailmen head coach Sammy 'Pamzo' Omollo is confident his team can get all the three points against the former champions.
"It is a tough match that is for sure. Gor Mahia have been having a good run, winning four straight matches and conceding one goal. We have been consistent since the start of the season, and that to us is an advantage, at least it shows that we are serious in the title race," 'Pamzo' told Goal on Tuesday.
"They have opened a gap between us and the only way we can reduce it is by winning this match. Last time we managed to get a point against them. Remember we scored first, they equalized later on, so this time round we want to ensure it does not happen."
Posta Rangers are third on 34 points, and a win will reduce the gap between them and Gor Mahia to three points.