The Green Army opted to start Kevin Omondi, in place of the injured Jacques Tuyisenge, to partner Meddie Kagere up front. K'Ogalo settled early trying to get an opener within the first few minutes, as the visitors looked out of place.
Poor passing was the order of the day from the visitors, failing to go past the midfield as Ernest Wendo and Humphrey Mieno run the show.
It needed the Dylan Kerr coached side five minutes to test the goalkeeper. George Odhiambo released Godfrey Walusimbi in the left flank, and the Ugandan did well to find Omondi in the danger zone, the latter made a good turn only to shoot straight at the goalkeeper.
In the 17th minute, the hosts again got another opportunity to test the opponents defense. Meddie Kagere was fouled and Francis Kahata delivered a sumptuous ball that was unfortunately cleared off the line by Mokuy Asterio.
Gor Mahia continued pressing and the efforts paid dividends in the 22nd minute. Kagere went past two defenders, crossed the ball to Kahata who chested it down for 'Ade' to open the scoring.
A few minutes later, it could have been 2-0; a Vegetarianos defender was adjudged to have handled the ball in the danger zone, leaving the referee with an easier option of pointing to the penalty spot. However, a tamely taken kick by Mieno was well saved by Sapunga Manuel, who parried the ball to safety.
Numerous chances were created but it seems K'Ogalo had forgotten their scoring boots at home. Five minutes after the break, Gor Mahia could have doubled their advantage, but once again, Francis Kahata's feeble shot failed to beat the goalkeeper.
Mieno, Kagere and Odhiambo were all guilty of missing good scoring chances. Substitute Ephraim Guikan made things right for his side with his first touch in the 62nd minute.
The Ivory Coast man, who replaced Odhiambo, was fed well from the right, and he muscled his way past the markers to get his name on the score sheet.
Despite possessing and running the show, good goalkeeping by Sapunga and poor finishing by Gor Mahia ensured no more goals scored.
The Kenyan champions will now need a draw of any kind in the second leg to proceed to the next round of the competition.
Gor Mahia Starting XI: Boniface Oluoch (GK), Wellington Ochieng, Harun Shakava, Ernest Wendo, Godfrey Walusimbi, Joash Onyango, Humphrey Mieno (78' Lawrence Juma) Francis Kahata, George Odhiambo (60' Ephrem Guikan), Meddie Kagere and Kevin Omondi (71' Samwel Onyango)
Unusued Subs: Shaban Odhonji (GK), Philemon Otieno,Charlee Momanyi, Cercidy Okeyo, Wesley Onguso and Bonfice Omondi.