Britain's women suffered a 2-1 loss to hosts Argentina in their opening Pool B fixture at the Hockey World League Final in Rosario.
Lily Owsley gave GB an early lead, but Maria Granatto drew the scores level at the end of the first quarter.
Agustina Habif then struck the winner in the third period.
In Pool A, world and Olympic champions the Netherlands looked in ominous form, thrashing Germany 5-1, while New Zealand beat South Korea 3-1.
Olympian Helen Richardson-Walsh collected her 100th GB cap in Britain's defeat.
"I'm joining an illustrious group of women and that's something I'm really proud of," she told BBC Sport.
"We've lost today which is really disappointing because it was a really big challenge for us, but we've won other big matches and we have the strength to come back."
Buoyed by the partisan crowd, Argentina began the stronger, but crafty wing play by Susannah Townsend allowed Owsley to poke home the opener with her first touch of the tournament.
Britain occasionally threatened to extend their lead, but the hosts maintained control for much of the match.
Argentina's second penalty corner brought the scores level and while GB were able to thwart four further efforts, a seventh proved too far with Habif firing in a rebound for the winner.
Australia share the lead of Pool B with the hosts after the opening round of fixtures, beating China 1-0 earlier in the day. GB will take on China on Sunday (21:45 GMT).
All four nations in the pool will make the quarter-finals, with group-stage results used to determine seedings in the first knock-out phase.