Trailing 15-12 at halftime, East Coast coach Ngarimu Simpkins gave his side a serve during the break.
"I told the boys at halftime if we didn't improve our discipline we were going to lose a game we could win," said Simpkins.
Tipoki put the Coast ahead for the first time in the game seven minutes into the second half with a superb try, only for Reynolds to land his sixth penalty from the restart.
Tipoki was also involved in the Coast's second try to Vorsenasu, converted by in-form first five Clayton Kiwara.
Another Reynolds penalty was followed by a try to fullback Lance Easton, which levelled the scores 26-26 with 16 minutes remaining.
Simpkins then turned provider with a cut-out pass to Vorenasu to seal the Coast's fourth win of the championship.
Although not on the scoresheet, Coast winger Mike King was outstanding. Lively Thames Valley halfback Mike Smith caused the Coast problems with his darting runs from the base of the scrum and Reynolds' goalkicking was superb.
East Coast 31 (Sikeli Vorenasu 2, Rua Tipoki tries; Clayton Kiwara 2 cons, 4 pens) Thames Valley 26 (Lance Easton try; Joe Reynolds 7 pens). HT: 12-15.
- APNZ