The United States finally clicked into gear with almost three quarters of the match behind them to beat Japan 30-17 and boost their Rugby World Cup quarter-final hopes.

Japan produced an outstanding performance to lead 5-3 at halftime after facing a strong wind through the first spell.

The United States seized their first lead with a try to Joanna Kitklinski in the 45th minute but Japan responded with a try to winger Hinano Nagura to lead 10-8 with 30 minutes remaining.

After a 22-10 loss to Italy in the first round of group matches last weekend, the US had to win on Saturday to keep their realistic chances alive of progressing to the knockout rounds.

The US attack was sluggish in the first 50 minutes, while both teams were wayward at lineout time, but they finally came together and finished with three tries and 17 unanswered points.

Japan winger Komachi Imaguchi scored a brilliant solo try four minutes from fulltime but the United States extended their lead with a late penalty.

"We just came out with a little more belief this time around," US captain Kate Zackary said. "We came here to have a performance, we needed a performance and the girls showed up. We needed to shine in that second half and every player did, one through 23."

Japan are without a win after two games in Group B, losing to Canada in their first match.