Leopards ran riot against a Forest side after the visitors took the lead early in the first half.
Talisman Ezekiel Odera scored a brace to put Ingwe in a pole position of defending the title.
Odera headed Ingwe ahead in the seventh minute before completing his brace, four minutes to the break after he was set by Brian Marita.
Jaffery Owiti doubled Ingwe’s lead after he went goes past his markers only to plant the ball in the far-right corner of the post.
Odera completed his brace with Ingwe’s third after he beat the opponent's offside trap to slot in his second of the match.
Ray Omondi completed the job with a fourth goal late in the dying minutes to hand Ingwe a safe passage into the round of 16.
Meanwhile, Vihiga United advanced to the FKF Shield after beating Vegpro 4-0 away at the Karuturi Grounds.
Captain Bernard Ochieng and Patrick Okullo gave the Kenyan Premier League side the lead in the opening half before completing the job with two more goals in the second half.
Dennis Wafula extended Vihiga’s lead with a third goal in the 67th minute before Jackson Simiyu converted a fourth from the spot after Juma Simon handled the ball inside his own box.