Young Gold Coast winger Dominic Peyroux scored in the final seconds to deliver the Cook Islands a remarkable 24-22 Pacific Cup victory over World Cup semi-finalists Fiji.

A late sideline conversion by Fijian captain Wes Naiqama had appeared to have given the Bati victory but the plucky Islanders refused to give in and eventually secured the shock victory off a high kick to the corner for the Titans under-20s player to score his second try of the game.

"It just proves that it's not over until the fat lady sings," said Naiqama.

"We're really disappointed but the Cooks played a great game and you've got to give them credit."

The Cook Islands entered the tournament as underdogs, having only qualified through a shock playoff victory over Samoa last week.

The victory secured them a place in the tournament final next Sunday, against either Papua New Guinea or Tonga, and puts them just one win away from a berth in next year's Four Nations tournament against Australia, New Zealand and England.

"It was a really good effort defending our line for so long, and to be able to come and win the game at the end was a great effort from the boys," said Cook Islands coach and former Australian Test forward David Fairleigh.

On a hot and windy afternoon at Lloyd Robson Oval, the Cook Islands started the stronger, building a 10-0 lead thanks to some enthusiastic attack from their team of mainly Toyota Cup (NRL under-20s) players.

Fiji's experienced NRL campaigners took a while to find their rhythm, but Newcastle winger Akuila Uate opened the scoring for the Bati after 20 minutes as he powered over in the corner.

Fiji levelled the scores minutes later when Ryan Millard set up the position for a Lepani Waqa try, creating a 10-all halftime deadlock.

The Cook Islands re-built their 10-point lead early in the second half, as Peyroux and halfback Daniel Fepuleai crossed for tries.

Fepuleai finished the game with two tries and two conversions for 12 points and man of the match honours.

Fiji's handling skills seemed to suffer under pressure as they made a string of errors but, with just over 10 minutes remaining, they mounted an impressive comeback.

First Uate burrowed over for his second try, before a series of probing attacks resulted in Leeds Rhinos centre Mike Ratu forcing his way through the Cook Islands defence to level the scores at 20-all.

Captain Naiqama then converted superbly from the touchline in windy conditions, and last year's World Cup semi-finalists thought they were through to the tournament finale.

But the Fijians twice knocked on in their own half in the final three minutes, and the effort of consecutive defensive sets eventually left a huge gap on the wing for Peyroux to gather a high ball in the in-goal area and score the Cook Islands' match-winning try with seconds remaining.