"This game is a whole different kettle of fish and everything has to be left on the line.
"Yes we had a great win against Arataki but they now have nothing to lose and this is a one off game.
"So we must keep a strong structure and shape throughout the game and go in with the right mind set of securing a win."
Irihei said the club had been disappointed to drop down from the top tier but stressed the importance of finishing off the season "properly".
"We let ourselves down, and there were a few performances where we really weren't good enough. Those results came back to haunt us," he said.
"But we have fully adjusted since coming into the second tier and our aim was to show that we are a top premier grade side.
"I think our recent displays have shown that but we have to make sure we complete this.
"Our ambition was always to win this and we have the home advantage in our favour so we have no excuse."
Whakarewarewa will be strengthened by the return of Kimo Houltham, Reuben Vaipou and Chris van der Vlugt, but will be without Jordan Lay (dislocated knee) and Joe Savage who is unavailable.
Irihei said he expected his side to be dangerous up front but was wary of Arataki's midfield combination.
"Our forwards have been dominant this year and we need to have that strong pack leading us out," he said.
"But I am aware that Arataki have an excellent inside-centre duo which the players must deal with.
"I"m expecting them to be a little weaker on the edges and we will look to exploit that."
Whakarewarewa have the best attacking record in the division tallying 335 points in Premier 2 whilst today's opposition have scored 238 points.
"We have managed to turn attacking positions into points and this will be crucial once again," said Irihei.
"The impressive back line have put a lot of points over for us so the forwards need to make sure they secure the ball well and set it up.
"Our quick players should hopefully do the rest. And I don't want us to take our foot off the pedal."
Tomorrow's semifinal games:
Baywide Premier 1:
Kick-off 2.45pm
Mount Sports v Rotoiti at Mount Sports at Blake Park
Rangataua v Tauranga Sports at Ariki Park
Baywide Premier 2:
Kick-off 2.45pm
Whakarewarewa v Arataki, Puarenga Park
Paroa v Poroporo, Lawson Park
Baywide Premier 1 Development:
Kick-off 1pm
Te Puna v Tauranga Sports, Maramatanga Park
Mount Sports v Te Puke, Blake Park
Baywide Premier 2 Development:
Kick-off 1pm
Opotiki v Arataki, Princess Street Reserve
Waikite v Poroporo, Bellvue Road
Baywide Division 1:
Kick-off 2.45pm
Judea v Kahukura, Maharaia Winiata Park
Rangiuru v Te Teko, Centennial Park
Baywide Division 2:
Kick-off 2.45pm
Waimana v Matata, Waimana Domain
Murupara v Eastern Districts, Ngati Manawa Park