Samoa withstood a formidable Cook Islands side to win 50-45 in Papakura.
Frances Solia's team established a five goal buffer after the opening quarter before the Black Pearls briefly drew level early in the third period.
However Samoa quickly re-established their advantage before closing out a third straight victory of the Oceania Qualifiers.
Meanwhile Fiji outclassed Papua New Guinea 55-34 in the later match to also make it three successive wins and join Samoa in sealing their spot at next year's World Cup in Liverpool.
