Bernard Ondiek scored the opener for Gor Mahia before Posta Rangers equalised just before the half-time break through Peter Nganga.
The visitors nearly opened the scoring in the fifth minute through Nicholas Kipkrui's header from a Samuel Onyango corner, but Gradus Ochieng in the Rangers goal denied the K'Ogalo forward with a fine save at this right-hand post.
Kipkrui incessantly complained when the referee failed to award him a penalty after he was brought down by Ochieng in the 13th minute. The former Zoo FC striker was put through on goal by Erisa Ssekisambu and managed to beat the goalkeeper before he was tripped.
Referee Hassan Athman waved play on, though, leaving the bewildered Gor Mahia striker objecting while on the ground.
Ondiek, who has not been a regular starter this season, broke the deadlock in the 38th minute when he beat the Rangers backline with his jump and found the back of the net with an accurate header.
Felix Ochieng could have equalised for the Mailmen in the 39th minute but his effort hit the side net.
Five minutes later, Peter Ng'ang'a brought the hosts level after he headed past Boniface Oluoch in the Gor Mahia goal, who could do nothing as he was shielded from full view by his defenders.
An in-form Onyango almost scored the second for Gor Mahia in the 66th minute but his effort from the left flank was off target.
Ochieng had a great chance to give Rangers the lead in the 75th minute when he blasted over the bar from close range after being played in by John Nairuka.
Neither side were able to create any clear-cut chances in the final 15 minutes.
Posta Rangers XI: Gradus Ochieng, Charles Odette, Jockins Atdo, Mbugi Joseph, Gershon Likono, Collins Omondi, Francis Nambute, Felix Oluoch, Peter Ng'ang'a, Simon Mbugua and Ken Mutembei.
Subs: Eliud Emase, Mugo Ezekiel, Santo Jerry, Tera Luis, Nairuka John, Mutembei Ken and Brian Osumba.
Gor Mahia XI: Boniface Oluoch, Pascal Ogweno, Geoffrey Ochieng, Charles Momanyi, Harun Shakava, Cercidy Okeyo, Erisa Ssekisambu, Bernard Ondiek, Francis Mustafa, Samuel Onyango, and Nicholas Kipkirui.
Subs: Shaban Odhoji, Philemon Otieno, Joash Onyango, Godfrey Odhiambo, Ombija and Jacques Tuyisenge.