The Knights scored after a just a few minutes of play when Kurt Gidley crossed and converted his own try.
Brad Tighe also posted a four-pointer for the Knights, but Penrith came back through Paul Aiton and Trent Waterhouse and it was the Panthers who led 12-10 at half-time.
The second-half was greeted with torrential rain. Nevertheless, both sides handled the conditions well with some excellent plays at both ends of the field.
Newcastle, who were without key personnel in half back Andrew Johns and hooker Danny Buderus, scored again in the second half when Cory Paterson went over.
But Penrith struck back through Geoff Daniela to make 18-all with 15 minutes to go.
19-year-old five-eighth Jarrod Mullen then rose to the occasion. A superb kicking game from Mullen and a brace of tries to Terrence Seu Seu ultimately securing victory for the Knights.
KNIGHTS 30 v PANTHERS 18 Scorers Knights: T Seu Seu 2, A Uate, K Gidley, B Tighe, C Paterson tries. K Gidley 3 goals. Scorers Panthers: P Aiton, T Waterhouse, G Daniela tries. P Wallace, L Rooney, K Peters goals. Richardson Park, Darwin, NT Crowd: Approx 9,000 7.30pm HALF TIME: Panthers 12-10 FULL TIME: Knights 30-18