Before the match, the dockers had gone 22 matches undefeated and the run looked set to continue against struggling Gatundu.
However, the leaders would get the shock of their lives as Gatundu played a tactical and consistent game throughout to come out on top.
Bernard Wafula was the toast of the day for Gatundu, as he scored on 68 minutes to silence the visitors.
The dockers retain the leadership of the division, with a 13 point lead over second placed Bidco United, but the industrialists have three games in hand.
Gatundu on the other hand, move just above the relegation zone.