But Counties Manukau made it an eight-point game when Paul scored her second try of the match.
This time she would not be successful with the conversion and Waikato led 20-12 midway through the second half.
The final 15 minutes belonged to Waikato with Esther Tilo-Faiaoga and Lonita Ngalu-Lavemai both crossing the line. Ruruku converted one out of two conversions as Waitomo Group: Waikato FPC finishing the game 32-12.
The victory sees Waikato finish the regular season in second place and will face the Auckland Storm again back home at FMG Stadium Waikato for a semifinal on Sunday, September 4. Kick-off is scheduled for 1.35pm.
Counties Manukau 12 (Mererangi Paul 2 tries; 1 conversion)
Waitomo Group: Waikato FPC 32 (Merania Paul, Rina Paraone, Esther Tilo-Faiaoga, Lonita Ngalu-Lavemai tries; Calista Ruruku 3 conversions, 2 penalties)
HT 7-17