Horgan comes into the side in place of Tyrone Howe while the only other backline change, sees Girvan Dempsey return to the full-back position.
Up front Eric Miller has made an extraordinary recovery and will fill the number eight berth with Alan Quinlan preferred to Kieron Dawson and Quinlan's Munster colleague Marcus Horan returning to the front row at the expense of Justin Fitzpatrick.
Ireland (v Samoa, Apia, Friday, 3.30).
Girvan DempseyJohn KellyMike MullinsJonathan BellAnthony HorganRonan O'GaraGuy EasterbyMarcus HoranShane ByrneReggie Corrigan capt Leo Cullen
Replacements. Paul ShieldsEmmet ByrneDonncha O'CallaghanAiden McCullenBrian O'MearaPaul BurkeGordon D'Arcy.