Okoth struck in the 69th minute to hand the defending champions their fourth consecutive league victory, taking K’Ogalo to 12 points from four matches and strengthening their grip on the top of the standings.
The victory also underlined Gor Mahia's growing confidence under head coach Charles Akonnor, whose second-half substitutions proved instrumental in breaking down a stubborn Homeboyz side that had threatened to frustrate the visitors.
Gor Mahia arrived in Kakamega determined to protect their perfect record, having won their opening three fixtures, while the hosts were hoping to secure their second victory of the campaign and close the gap on the league leaders.
The visitors made a lively start and nearly took an early lead in the sixth minute when Daniel Sakari picked out Musa Shariff, but Homeboyz goalkeeper Ibrahim Wanzala reacted sharply to keep out the forward's effort.
Wanzala was called into action again four minutes later, denying Alpha Onyango after the midfielder combined well with Ebenezer Ocran and Shariff in a promising attacking move.
Homeboyz gradually settled into the contest and created opportunities of their own. Ibrahim Joshua failed to make the most of a delivery from Collins Odhiambo, while Glen Otunga sent his attempt narrowly wide after being released by Thomas Omolle.
Okoth, facing his former club, threatened midway through the first half when he beat his marker and fired a low effort that was cleared by Charles Momanyi.
Gor continued to press for an opener, with Paul Okoth testing Wanzala following an attacking move involving Sakari and Bryton Onyona.
The hosts remained dangerous on the counterattack, forcing Gor Mahia's defence to stay alert as both sides exchanged chances in an entertaining opening period.
Homeboyz goalkeeper Wanzala produced another important intervention before the break, punching away a delivery intended for Onyango, while Enoch Machaka fired over the crossbar from distance.
At the opposite end, Maurice Ojwang directed a header straight at Gor goalkeeper Humphrey Katasi before Omolle missed the target in stoppage time, leaving the teams level at halftime.
Gor Mahia returned from the dressing room with renewed urgency, and Machaka nearly broke the deadlock shortly after the restart when his attempted delivery struck the inside of the post.
Homeboyz responded through Otunga, whose effort forced Katasi into a fine save as the hosts continued to demonstrate their attacking threat.
With the match still finely balanced, Akonnor turned to his bench around the hour mark, introducing Ben Stanley, Ebenezer Assifuah and Jackson Dwang in a tactical move aimed at injecting fresh energy into Gor Mahia's attack.
The changes immediately improved K’Ogalo's attacking movement, with Stanley coming close to scoring after connecting with a delivery from Dwang, only to find the side netting.
The breakthrough eventually arrived in the 69th minute following another move involving the substitutes.
Stanley regained possession and released Dwang, who carried the ball forward before switching play towards the left flank.
Okoth collected the pass, advanced into the penalty area and unleashed a powerful left-footed strike that flew beyond Wanzala into the roof of the net.
The goal sparked celebrations among the travelling Gor Mahia supporters and proved particularly painful for Homeboyz, who had been undone by a player who previously represented the Kakamega-based outfit.
Akonnor praised the impact of his substitutes after the match, pointing to the players' ability to understand instructions and influence proceedings when introduced.
Those who come in, the changes that we make, they are slightly different from what we did last season. Sometimes people would come in and they would not be able to give their best. Today, this time around, we are very happy how they come and transform the game, change the game,” Akonnor said.
The Ghanaian tactician expressed satisfaction with his team's continued improvement, particularly the growing effectiveness of players coming off the bench.
They read the game very well, they come in, the instructions given to them, they are doing that. Gradually, I think we are progressing very, very well,” he added.
Despite falling behind, Homeboyz refused to surrender and pushed forward in search of an equaliser during the closing stages.
Clem Imbayi forced Katasi into another important intervention with a bouncing effort, while Boniface Nyabuto threatened to capitalise on a loose ball before Frank Odhiambo produced a timely sliding tackle.
Momanyi also had an opportunity to restore parity six minutes from time but sent his header wide after connecting with a corner delivered by former Gor Mahia player Boniface Omondi.
However, the visitors remained disciplined defensively, protecting their narrow advantage until the final whistle to complete another successful league outing.
Homeboyz head coach Edward Manoah admitted that his team had failed to make the most of its opportunities, acknowledging that poor finishing ultimately contributed to the defeat.
It's been a game of about four moments. In the first and second halves of the match we didn’t start well compared to our opponents. In the run of play, we conceded a goal from a very tight angle,” Manoah said.
The Homeboyz tactician challenged his players to show greater determination and improve their attacking efficiency as they seek to recover from their first defeat of the campaign.
But after conceding, we had a chance of coming back to the game, but we didn’t. I will just urge the boys to develop a very strong character and also work on attacking,” he added.
The result leaves Gor Mahia with a maximum 12 points from their opening four matches, temporarily establishing a seven-point advantage at the summit as they continue their pursuit of another league crown.
For Akonnor, the performance offered further encouragement that his tactical approach is beginning to produce the desired results, with his side demonstrating both attacking quality and the resilience required to grind out victories away from home.
Homeboyz, meanwhile, remain on four points with a game in hand and will be eager to rediscover their winning touch after suffering their first loss of the season.
With four wins from four matches, K’Ogalo have laid down an early marker in the title race, and their latest triumph in Kakamega sends a clear message to their challengers that the defending champions are determined to retain their place at the summit of Kenyan football.
