Mathare United suffered a major blow late in the second half after goalkeeper Job Ochieng' was shown a straight red card in the 79th minute.
Ochieng was given his marching orders after a foul on Lucas Waitere, a decision that forced Francis Kimanzi to play the remainder of the game without a striker.
The tactician had to make do without Clifford Alwanga, who was sacrificed for David Okello, who came in as a replacement for Ochieng in goal.
Cliff Nyakeya had given Mathare United the lead from the spot in the fifth minute before Alwanga doubled the advantage with a thumping header just nine minutes later after connecting to new signing Kevin Kimani's well-delivered corner.
Elsewhere, Kakamega Homeboyz welcomed KCB back to the league with a shocking 1-0 victory. The script was relatively different for Western Stima, the other league newbies, who beat Posta Rangers by the same score line away.