They may be defending champions, but the US lost their first game in the 12-team tournament to Argentina on Monday (October 1).

Since then they've defeated Italy, Poland, and now Japan, 25-19, 25-19, 25-20.

"I feel like Japan is the most improved team, maybe in the world," US head coach John Speraw said.

"They have great young players… we were ready for a team that plays very good defence and hits their serve very hard.

"They aren’t the biggest team in the world - they aren’t Russia or Poland.

"But we knew we were in for a fight tonight."

Blocker Max Holt was the star for the Americans, leading the way with 12 points at Marine Messe Fukuoka.

They now face Tunisia tomorrow, who are yet to win a game, before relocating to Hiroshima for the second round of matches, starting on Wednesday (October 9).

Still unbeaten and topping the table are Brazil, who defeated Russia at the White Ring in Nagano, 25-16, 25-22, 25-22 - they remain the only unbeaten team and will be relishing their next match against Iran.

Poland bounced back from their loss to the Americans with a battling 3-1 win over Argentina, 27-29. 25-17, 25-18, 26-26.

If Poland want to have any chance of taking top spot, it's essential they beat Italy tomorrow.

Five teams sit below Poland on third, on two wins and two defeats.

Tunisia remain winless at the bottom of the table, losing in straight sets to Italy.