An inspring performance from Alev Kelter led the USA to a bonus point victory over Japan to maintain their Pool B hopes after an error-strewn first half.
USA captain Kate Zackary said: “We came out with a little bit more belief in the second half. The girls know how important that second half was and put in a great display.”
Head coach Rob Cain named a physical lineup with Saracens star Kelter moving to centre following the 22-10 defeat to Italy.
Japan named a pack weighing 50kg less than the Eagles but they started relentlessly as a slick blindside lineout move created space for scrum-half Megumi Abe to touch down in the corner early on.
Kathryn Johnson was sin-binned for a deliberate knock-on but the USA's heroic defence refused to concede any points while a player down, with Gabby Cantorna scoring a penalty to bring the USA to within two at the break.
The match sparked into life on 45 minutes as Eagles' hooker Joanna Kitlinski raced into the corner to finish a move started by Cantorna's chip. Japan wrestled back the lead as a quick penalty allowed Hinano Nagura to score in the corner, before the USA went over again three minutes later as Kelter outmuscled three defenders to score.
Another intelligent grubber by Cantorna then released replacement flanker Elizabeth Cairns to score in the corner with her first touch before Jennine Detiveaux crashed through a tiny gap to secure the bonus point.
Japan wing Komachi Imakugi reduced the deficit with a mazy run but then saw yellow for a deliberate knock-on, with Kelter notching the resulting penalty from out wide to bring her tally to 12 points.
TEAMS
USA: Bizer 6 (Clapp 60, 7), Detiveaux 7, Haungatau 5, Kelter 9, Feury 6, Cantorna 8 (Foster 60, 7), Ortiz 7 (Waters 55, 7), Rogers 8 (Benson 77), Kitlinski 7 (Treder 77), Jacoby 6 (James 55, 6), Sommer 7, Ashenbrucker 6 (Kronish 77), K Johnson 5 (Cairns 60, 7), R Johnson 8, Zackary 7 (c)
JAPAN: Matsuda 6 (Nagai 71, 6), Nagura 6, Furuta 5, Yamamoto 7, Imakugi 6, Otsuka 7, Abe 7 (Tsukui 63, 5), Minami (c) 5 (Kitano 63, 5), Taniguchi 4 (Komaki 63, 6), Kato 6 (Kitano 71, 6), Sato 5 (Tamai 63, 6), Takano (Yoshimura 63, 5), Nagata 5, Hosokawa 6 (Nagai 63, 6), Saito 7
REFEREE: Amber McLachlan (Aus)
