The Tala scored a comfortable win over Papua New Guinea, 89 - 28, to follow up on their victories over Samoa and Fiji.
Tonga are top of the table with six points while three other teams all have two points, after one win apiece.
The Tala play their fourth and final game on Friday night, against the Cook Islands.
Meanwhile, Samoa secured its first victory of the competition, beating the Cook Islands 54 - 35.
The top two teams qualify for the World Cup finals being held in Cape Town, South Africa next year.