John Strange handed his son Ethan his Australian jersey in the Townsville sheds before the 22-year-old's international debut.
"My dad's not a very emotional person, so to see him in that state, it caught me off guard," Strange said.
The Canberra five-eighth had been holidaying in Thailand when Mitch Moses was injured in Australia's World Cup opener against New Zealand.
Kangaroos coach Kevin Walters called him into camp, prompting Strange to cut short his trip and join the squad before its match against Fiji.
He made his debut against the Cook Islands last Saturday, entering after half-time as lock, a position he had played for barely five minutes in his career.
"I was in Thailand two weeks ago, and now I have played for Australia, so I'm pretty happy," Strange told NRL.com.
Strange set up a try, kicked a conversion and made 13 tackles in 36 minutes, though he said the defensive workload left him tired.
Eligible for England and New Zealand, he chose Australia, saying, "I was born and raised on the NSW Central Coast. I don't know if it would have felt right to play for another country."
His debut followed a breakout year: he played in all three State of Origin games for NSW, starting Game One alongside Nathan Cleary before coming off the bench in the next two.
Strange has kept his place on Australia's bench for Sunday's semi-final against Samoa, with his role still uncertain.