The Rock recovered from an eight point deficit, in yesterday's first semi final at Cabramatta in Western Sydney, to defeat Greece, 16-8.
Greece opened the scoring with a 19th minute penalty and extended their lead to eight points when Latrell Schaumkell spilled a kick through on the final tackle to gift the Titans a try in the 25th minute.
Niue hit back with a try of their own six minutes later through Wes Lolo, who fended off one defender and stepped inside another to cut the deficit to two points at the break.
Coach Brendan Perenara said his players were given clear intructions at the interval.
"The message at half-time was just play to our strengths, play up the middle and don't go away from it," he said.
"We were playing too much on the edge in the first half so [we decided] at half-time play to our strengths up the middle and keep on going through them."
Niue took the lead six minutes into the second spell when Zebastian Luisi busted through the Greek defence to set up Justice Utatao in the left-hand corner.
Cyruss Payne finished off a flowing move from a scrum to score Niue's third in the right-hand corner ten minutes later, in what proved to be the final scoring play of the game.
Perenara was proud of the way his team fought back to close out the game.
"It was a bit of a grind and especially the first half I think we ran away from our strengths," he said.
"I think we found that out and regrouped and put it into the second half, went to our strengths and it paid off."
Niue will take on Malta in Saturday's grand final, who they beat 26-16 in their first match of the competition.
Meanwhile, Vanuatu were thrashed 44-4 by Poland last night and will face Turkey in the seventh place playoff.