Niamh Briggs scored 18 points as Ireland's women opened their World Cup campaign with a battling 23-17 victory over the USA in France.
Full-back Briggs scored a first-half try and also kicked 13 points as the Irish fought back from conceding an early try to win in Marcoussis.
Lynelle Kugler's try put the US ahead, but Ailis Egan and Briggs touched down as Ireland led 20-10 at half-time.
A Carmen Farmer try cut Ireland's lead before Briggs slotted another penalty.
Ireland won last year's Six Nations title, but Friday's game was regarded as a stern test against the world's fifth-ranked team, who won the 1991 World Cup.
The Irish will face New Zealand in their second Pool B game on Tuesday.
Only the pool winners will be guaranteed a semi-final place, but with Ireland facing Kazakhstan in their last group match on 9 August, two wins should be enough to progress as the best runners-up.
Ireland captain Fiona Coghlan:
"There are aspects we need to improve on and we'll look at that going into the New Zealand game.
"But I think when you're down, the ability to come back, go down and again and come back, that shows what this team is made of and the character that's in the team.
"Particularly in the last 10-15 minutes, we were all on the same page and everyone knew what we had to do in order to get the win. We'll take great heart from this win."
USA: Meya Bizer; Vanesha McGee, Akalaini Baravilala, Emilie Bydwell, Sadie Anderson; Kimber Rozier, Jocelyn Tseng; Hope Rogers, Katy Augustyn, Jamie Burke, Carmen Farmer, Sarah Walsh, Jillion Potter, Lynelle Kugler, Kate Daley.
Replacements: Kittery Wagner, Sarah Chobot, Sarah Wilson, Sharon Blaney, Shaina Turley, Deven Owsiany, Hannah Stolba.
Ireland: Niamh Briggs; Ashleigh Baxter, Lynne Cantwell, Grace Davitt, Alison Miller; Nora Stapleton, Tania Rosser; Fiona Coghlan, Gillian Bourke, Ailis Egan, Sophie Spence, Marie Louise Reilly, Siobhan Fleming, Claire Molloy, Heather O'Brien.
Replacements: Sharon Lynch, Fiona Hayes, Laura Guest, Paula Fitzpatrick, Larissa Muldoon, Jenny Murphy, Jackie Shiels.