The goalkicker took his time to go through his normal routine and begin his run up.
An instant after kicking the ball, Ririnui threw his hands in the air and was swamped by his teammates. Pandemonium erupted and Whaka won the game 22-21.
An ecstatic Ririnui after the match said he did not feel any added pressure before the kick.
"We had a scrum and the ref said 'last play'. I was thinking we would just keep the ball alive with pick and rolls, but we scored in the corner which made it hard on myself," he said.
"I have been in a similar situation a few times. I just went through my normal kick routine and didn't think of the pressure at all. As soon as it hit my boot, I was celebrating straight away."
In an added twist, he had not planned on playing on Saturday.
He injured his shoulder about six weeks ago and was going to make his return a bit later in the season.
"The coach said 'if it comes down to crunch time, we will get you out there'."
Despite losing the match, Rotoiti played the better rugby in the terrible conditions and were unfortunate not to go on and win the game.
They raced away to a 16-5 lead in the first half with a try to prop Jacob Marsters and three penalties to Tyson Ripia.
Whaka pulled back a penalty on halftime to close the gap to 16-8.
The second half began with a try to Whaka's Whaimotu Craft-Chemis.
Rotoiti forward Joe Royal replied with a try shortly after but it would be Whaka's day, scoring the late winner and conversion.
The win means Whaka leap-frog Rotoiti into the top four and also hold onto the Tai Mitchell Shield.
Whakarewarewa 22 (Riiki Waitoa, Whaimotu Craft-Chemis, Kimo Houltham tries; Te Rangi Fraser con, pen, John Ririnui con) defeated Rotoiti 21 (Jacob Marsters, Joe Royal tries; Tyson Ripia con, 3 pen).