Great Britain were beaten 3-2 in the first of three Tests against Argentina, despite a debut goal from Alan Forsyth.
Sam Ward also found the net but two goals from Matias Paredes and Gonzalo Peillat's penalty corner sealed victory for the visitors at Bisham Abbey.
"We fell right into their trap as we were sloppy at times in possession which allowed them to counter-attack," said GB head coach Bobby Crutchley.
"That's what they're looking for and that's why it's frustrating."
The series is helping Britain prepare for the World League Final, which starts on 27 November in India.
The second Test against Argentina is on Wednesday, also at Bisham Abbey.