With the contest locked up at 32-32 with only two minutes left, the Vodafone Junior Warriors fed off a Penrith error to surge onto attack, creating the vital touchdown for halfback Malu.
With 29 previous appearances, Malu was in the side replacing injured first-choice No 7 Mason Lino and could hardly have picked a more critical moment to make such a telling contribution.
Centre Solomone Kata, taking over the goal-kicking duties from Lino, slotted the conversion to give the Vodafone Warriors their most important victory of the year so far.
At Centrebet Stadium, Penrith
Penrith Panthers 32 (Jarred Wilson 2, Waqa Blake, Sam Scarlett, Bryce Cartwright, Dallin Watene-Zelezniak tries; Bryce Cartwright 4 conversions).
Vodafone Junior Warriors 38 (Alamoti Finau 2, Raymond Faitala-Mariner, Tuimoala Lolohea, Albert Vete, Ngataua Hukatai, Eko Malu tries; Solomone Kata 5 conversions).
Halftime: 28-10 Vodafone Junior Warriors.
Referees: Ziggy Przeklaska-Adamski.
Vodafone Junior Warriors: Ngataua Hukatai; Alamoti Finau, Solomone Kata, David Fusitua, Metia Lesati; Tuimoala Lolohea, Eko Malu; Vince Afoa, Michael Sio, Albert Vete; Raymond Faitalaa-Mariner, Adam Tuimavave-Gerrard, David Bhana (c). Interchange: Kurt Robinson, Sam Lisone, Eric Newbigging, Kouma Samson.