The Young Boys in Green fell to a comprehensive 3-0 loss in Waterford ahead of the Uefa U19 European Championships qualifying
Despite carving out a number of chances early in the game, the Young Boys in Green eventually succumbed to the superior finishing of their Slovenian counterparts.
Ireland's only real chance of note came early in the game when Manchester United striker Sam Byrne unleashed a low shot from edge of box, but his effort was comfortably saved by goalkeeper Gregor Zabret.
Indeed, it was to be a crucial miss as the visitors took the lead minutes later as Dino Hotic stepped up to dispatch a curled free-kick past the despairing Shane Fagan. Slovenia then doubled their lead just before half time when Bian Paul Sauperl's long-range shot was adjudged to have crossed the line after striking the cross-bar.
Ireland struggled to get into the game in the second half and Slovenia made it 3-0 early after the re-start. Determined running from Luka Zahovic opened up space to allow the winger to put in low cross for Luka Gajic, who tapped in from close range.
The Republic of Ireland U19s will take on Slovenia in the second of their friendly fixtures on Thursday, September 5.