Mandonga took the fight to Wanyonyi and descended on the latter with a flurry of punches that left the Kenyan clutching on thin air.
Wanyonyi had nowhere to hide as Mandonga turned him into a punching bag.
Confident Mandoga controlled the tempo of the one-sided encounter as he wanted as confused Wanyonyi shifted from one corner of the ring to the other in search of reprieve.
The triumph took Mandonga's tally to five, including three knockouts and a draw.