The visitors went into the halftime break with a 19-10 lead but were outscored in the second half 17-13.
With 15 minutes to go, Whaka were leading 27-26 but up stepped Roberts to kick two late penalties to give the red-and-blacks their seventh straight loss.
Rotoiti also suffered a loss to Te Puna 32-17. The loss means Te Puna moves ahead of the lakesiders. However, they cannot be discounted despite losing their first match in more than a month. They will fancy themselves to pick up four-try bonus point wins against Rangataua and Paroa, but will probably also need some points from their match against Tauranga Sports in week 17 to qualify for the post-season.
In the other matches in the round, Tauranga Sport continue to lead the pack with a 33-14 win over Te Puke, Opotiki beat Paroa 38-20 and Mt Maunganui were too strong for Greerton beating them 43-20.
Division one saw Whakatane Marist beat Marist St Michaels 20-19, Te Teko draw with Kahukura 17-17, Rangiuru thrash Ruatoki 39-17, Poroporo narrowly beat Waikite 17-15 and Ngongotaha beat Katikati 20-10.
Scorers:
Rangataua 32 (T Gardiner, R Taupaurima 3 tries; D Groot 3 cons, M Roberts 2 pens) Whakarewarewa 27 (J Ririnui, D Pereira, A Mako tries; J Ririnui 3 cons 2 pens) HT: 19-10
Results for Bay of Plenty Rugby; Premier One:
Tauranga Sports 33 Te Puke Sports 14, Opotiki 38 Paroa 20, Te Puna 32 Rotoiti 27, Mount Maunganui 43 Greerton Marist 20, Rangataua 32 Whakarewarewa 27.
Premier Two:
Whakatane Marist 20 Marist St Michaels 19, Te Teko 17 Kahukura 17, Rangiuru 39 Ruatoki 17, Poroporo 17 Waikite 15, Ngongotaha 20 Katikati 10.