Rau's scoring antics started what was a frantic first 20 that saw both sides scrambling to keep the opposition out.
After the break, Hikurangi once again opened the scoring with another try out wide to Shelden McKinley, which was converted by Caleb Henare.
Takahiwai coach Shane Hool said there was a minor fight back from his side with tries to Nick Schuster and Hori Tuhoro, with a conversion to Wi Thompson, before Steve Rau and Kieron Wihongi-Henare put the game beyond doubt.
"Charles Tarau scored a consolation try to give a final score of 40-14 to Hikurangi," Hool said. "It was a fiery game at times with Naphatali Pumipi [Takahiwai] and Innocent Tuimavave [Hikurangi] both spending time in the sin bin for dangerous tackles."
Hool said stand out players were Takahiwai's Thompson, Tarau and Mike Hauraki. While for Hikurangi he credited Joe and Steve Rau, Kylie Walters and Henare.
In the weekend's other South Pool matches, Northern Wairoa Bulls snuck home against Portland by 32-30 while the City Knights came out on top of the Hora Hora Broncos 36-10.