In the 20th minute, Wallace put in a grubber kick which looked certain to go dead, only for Moylan to sensationally leap into the air - fortuitously stepping on Darius Boyd's shoulder to keep him off the ground - and batting the ball back into play.
Leilua was there to clean it up, but threw a ridiculous ball in his own in-goal, allowing Panthers winger David Simmons to touch down for a 10-4 lead.
The Panthers then scored on either side of halftime to stretch their advantage to 20-10, Leilua offending again when he attempted a no-look flick-pass which went nowhere near its intended target - with Penrith centre Dean Whare scooping up and racing 75m untouched to put the game virtually beyond doubt.
Leilua was also bundled into touch and threw a ball over the sideline.
Next week the Knights travel to Brookvale Oval to tackle high-flying Manly, and if they fall to a fourth-straight defeat, their season will be nearly impossible to rescue.
Queensland Origin star Boyd looked pedestrian at fullback and Jarrod Mullen's nice touches were to no avail.
Penrith are confident prop Plum isn't seriously injured, despite being stretchered off the field and put in a neck brace after colliding with Mullen's shoulder in a tackle attempt.
Despite coming off second best, Plum was placed on report for the reckless nature of his hit on Mullen, who was kicking.
- AAP