Ireland suffered a second defeat in two days at the Champions Challenge 1 after losing to Japan in Argentina on Sunday.
The Irish were beaten 4-3 by Argentina in their opener and sit bottom of Pool B after being punished for poor finishing by the Japanese in Quilmes.
Kazuhiro Tsubouchi, Tomonori Ono and Shinji Kawauchi netted for a clinical Japan team while Ireland squandered numerous chances.
Ireland face South Africa in their final pool game on Tuesday.
John Jermyn, Timmy Cockram and Michael Watt scored in the narrow defeat by the hosts on Saturday.
The Irish team's participation in Argentina had been in major doubt until a late fundraising campaign.
Ireland: D Harte, C Harte, Jackson, Gormley, Gleghorne, Magee, McCabe, McConnell, Caruth, Watt, Darling.