Chester Okoyo was credited with the all important goal straight from a corner kick on the stroke of half time to seal victory in the open match that could have swung either way as the military men moved to within three points of leaders Tusker.
Mathare, who are still stuck on 13th, have themselves to blame for not taking their chances in the second period as both sides went for each other.
Innocent Mutiso was their main culprit after spurning two glorious chances to level the match, the first, five minutes after the break when his storming run to the box saw him attempt to shoot from a tight angle.
After the initial shot was repelled, he tried a cut back to the box but the Ulinzi defence cleared.
On the other end, Stephen Waruru and Lawrence Owino had chances to make the game safe but Mathare keeper, Joseph Ruto made a flying save from the latter when he collected the ball in the box and sent a powerful shot that was sailing to the bottom corner.
Okoyo’s effort timed at 46 minutes that appeared to be helped to the net by the faintest of touches by team mate and captain Evans Amuoka proved to be the difference as the defending champions moved to 38 points, three shy of Tusker.
KPL resumes this weekend with the Brewers visiting Thika United on Sunday where a victory will restore their six point cushion.
Gor Mahia, who were dislodged from second spot by Ulinzi have a seemingly easy assignment against relegation candidates, Congo United at City Stadium on Saturday.
Elsewhere on Saturday, City Stars entertain KCB at Hope Centre, Sofapaka face Werstern Stima, Bandari welcome AFC Leopards in Mombasa as Chemelil renew acquaintances with Rangers.
Sony Sugar face Karuturi Sport in the only other Sunday match in Awendo.