Earlier, Western Stima forced the Brewers to another one-all draw in Machakos in their previous meeting.
Sydney Ochieng was brought down by Francis Omondi inside the penalty area and the referee, rightfully, awarded Tusker a spot-kick. David Majak, who was making his full debut for the visitors, converted from the spot to open his KPL goal account in the 15th minute.
Mathare United won their own penalty four minutes later when Marlon Tangauzi, who was making a return to the starting XI, handled the ball inside the area as he attempted to clear under pressure.
Cliff Nyakeya made a successful conversion to square the match at 1-1. That was Nyakeya’s sixth goal of the season to draw him level on goals scored with Enock Agwanda and Derrick Otanga of Sony Sugar and Gor Mahia’s Nicholas Kipkirui.
Klinsmann Omulanga had two fine chances in the 21st and the 26th minutes, but both of his efforts slid wide after he found himself in a pocket of space on both instances.
Sydney Ochieng was denied by Mathare United’s goalkeeper David Okello as he attempted a curled effort from just outside the box two minutes before the end of the first half.
Majak found himself through on goal six minutes after the resumption, but his cutback - intended for Ochieng - was too short and allowed Okello to collect the rolling ball in front of him.
Tusker suffered a blow in the 80th minute when Rwandan goalkeeper Emery Mvuyekure was sent off after the assistant referee ruled that he handled the ball outside his area.
Robert Mboya was summoned to take charge of the visitors' posts, but Mathare squandered the free kick won in the process.
The Slum Boys will host Sony in their next match while Tusker will be at Kenyatta Stadium to host KCB for KPL week 22 action.
Mathare United XI: David Okello, David Owino, James Situma, Johnstone Omurwa, Andrew Juma, Francis Omondi, Cliff Nyakeya, Chrispin Oduor, James Kinyanjui, John Mwangi, Klinsmann Omulanga.
Subs: Job Ochieng, Ronald Reagan, Roy Oakl, Alphonse Ndonye, Roy Okal, Tyson Otieno and Kelvin Kimani.
Tusker XI: Emery Mvuyekure, Eric Ambunya, Hillary Wandera, Justin Omary, Marlon Tangauzi, David Naftali, Kevin Wafula, Boniface Muchiri, Jackson Macharia, Sydney Ochieng and David Majak.
Subs: Mboya, Aloro, Odhiambo, Nzuki, Madoya, Adwar, Omondi.