The Somerville Theatre was packed to the rafters Saturday night for the world premiere at the Irish Film Festival Boston of “Rocky Ros Muc,” the documentary about Sean Mannion, who grew up in the sleepy village of Ros Muc in the Irish-speaking region of Connemara in the west of Ireland and became a great boxer while living in Dorchester and training in South Boston. It’s a bittersweet tale, as much about immigration and separation as it is about boxing at the highest level. At the film’s conclusion, the audience gave Mannion a long, loud standing ovation. Mannion joined director Michael Fanning, producer Maire Bhreathnach, and his biographer, Ronan Mac Con Iomaire, onstage for some more love. “I was more nervous about watching this than any of my fights,” Mannion said. The film was awarded best global documentary at the festival. Festival director Dawn Morrissey said it was the biggest crowd in the festival’s history. Probably the loudest, too. Up Galway!