New signing Klinsman Omulanga came off the bench to rescue the ‘Slum Boys’ with a match-winning goal in the 'Slums Derby' at the Utalii Grounds.
Mathare needed a second-half penalty and Omulanga’s header to register their maiden win in teh three day tournament.
Shawn Fila gave Kibera Blackstars the lead in the 60th minute, but Daniel Mwaura restored parity from the spot fourteen minutes later.
Omulanga, who is on loan from Liberty Academy, was pulled from the bench and the 19-year-old did not disappoint when he headed home the winner.
Mathare United will play fellow Kenyan Premier League side, Bandari in the last match of the day.
Bandari beat KCB in the opening match on Friday to take their win record to two having overcome a tensed moment to force a slim 3-2 win against hosts Kariobangi Sharks on Thursday.