Former SP Hunter and PNG Kumul forward, Henry Wan Noki got Tumbe on the board early in the 7th minute when he barged over to score.
The city boys hit back soon after winger Damien Herod snuck past the defence for a try.
Tumbe were impressive, dominating the remainder of the first half, crossing the line two more times through Israel Balio and Wari Molu.
Halfback Raven Jonah extended Tumbe's lead after kicking a penalty goal right in front of the sticks.
The score was left at 20-4 at the break.