Irankunda left German powerhouse Bayern Munich in July, knowing the value of playing minutes as Socceroos coach Tony Popovic pieced together plans for next year's World Cup.
There have been limited chances for the 19-year-old to shine for Watford in recent weeks, having dashed home at the start of this month for family reasons.
But the Australian has given a timely reminder of his talent to coach Javi Gracia in Norwich, lifting the club to a third straight win as they dream of promotion to England's top tier.
Irankunda entered the fray in the 79th minute, coming on for Othmane Maamma.
The fixture seemed destined to finish a scoreless draw until he conjured something from nothing with an eye-catching assist.
The speedster took possession and bust down the left wing, past his man and into the box.
As three Norwich defenders descended, the teenager delivered a pinpoint pass to fellow substitute Vivaldo Semedo.
Semedo's shot took a deflection and crashed into the back of the net.
"With so many games you have to make use of your substitutes and I thought they made the difference for us," Gracia said.
"They all made big contributions and for the goal, two of them were involved. I was delighted for Vivaldo who has worked very hard for us and got the goal he deserved."
Watford sit sixth on the Championship table, having lost just one of their past 12 games.
The top two clubs are promoted to the Premier League, with those ranked third to sixth pitched into a playoffs battle for the final spot in the top tier.
"This is just the first game of the second half of the season and I am not focusing on the table," he said.
"I am focused on my work, trying to improve the team day by day and I am sure the players are the same."
Australians Adrian Segecic and Callum Elder also produced goal assists on Sunday in the Championship, for Portsmouth and Derby County respectively.
Derby County lost 2-1 to Leicester City, while Portsmouth defeated Charlton 2-1.
Socceroos defender Cameron Burgess enjoyed a productive day in the Championship, helping Swansea City record a 1-0 win over Oxford United.
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