Birthday boy Siale Piutau dedicated a fitting Tonga swansong to his late sister after the Pacific Islanders beat the United States 31-19 in their final match of the Rugby World Cup.

The Tonga captain celebrated turning 34 on Sunday by scoring a try and slotting over the first conversion he has ever taken in a man-of-the-match performance at Hanazono Rugby Stadium.

A first win of the tournament ensured it was the USA rather than Tonga who finished bottom of Pool C.

Piutau was carried off the field by his team-mates after the game before paying tribute to his sister Ema, who lost her battle with stomach cancer in April.

"It’s been a tough journey, but all this has been done in her memory." said Piutau.

The centre added: "The boys have given me the best birthday possible. It's been a great honour to represent this jersey."

Piutau was relieved to hit the target after Telusa Veainu's bonus-point score as he was concerned that his final international appearance would be remembered for a different reason.

"I didn't want to take it [the conversion], but they insisted, and I certainly didn't want to miss it because I would have become an online meme." said Piutau.

The USA finished a second successive World Cup without picking up a point, having been 12-7 up at half-time.

Coach Gary Gold said: "It's pretty raw right now, but if it shows anything it's just how bloody difficult it is to win a game at the Rugby World Cup.

"The margin is very small between being competitive and getting a result."