Kodi Smit-McPhee wasn’t on the shortlist when director John Hillcoat started searching for a young boy who could hold his own opposite Viggo Mortensen in the postapocalyptic Cormac McCarthy parable “The Road.”

But according to the director, there was little, if any, doubt that the young Australian was absolutely the right choice for the extremely demanding role. “It came down to one kid, and then Kodi came in the room,” Hillcoat recalls. “In the middle of his audition, I knew he was the one.”

The only reason Hillcoat was even aware of Kodi, who just turned 12, was the trailer for “Romulus, My Father,” a family drama that won the Australian Film Institute’s best picture prize and earned Kodi the org’s Young Actor’s Award.

Hillcoat wanted an actor with a sense of independence, someone auds could imagine standing up to Mortensen on their hellacious journey. “He makes it more of a proper two-hander instead of just a father and poor little fella,” Hillcoat says. “If Viggo had to carry it all, it just wouldn’t work.”

Smit-McPhee’s older sister Sianoa is also an actress, appearing in HBO’s “Hung.”