Conor Bradley was named in Liverpool's starting XI to face Norwich City in the Carabao Cup on Tuesday night.
The 18-year-old from Co Tyrone becomes the first Northern Ireland player since Sammy Smyth in 1954 to play a competitive game for the Anfield Reds.
Bradley joined fellow Academy prospect Kaide Gordon in a new-look right side for Jurgen Klopp in Norfolk.
Gordon, who turns 17 in early October, becomes the fifth youngest player in Anfield history as Northern Ireland international Bradley took his place in the absence of Trent Alexander-Arnold.
Bradley featured in Klopp's squad during their pre-season tour of Austria and made his debut in the friendly against VfB Stuttgart.
Tonight will be the teenager's competitive bow for the Reds, and another defining moment in the young Northern Ireland defender's career.
Bradley recently made his senior international debut for Northern Ireland when he came off the bench to feature against Switzerland in a World Cup qualifier.
Tuesday's start against Norwich is the latest show of confidence from Klopp, who rates Bradley very highly.
Speaking to the Liverpool website after their tour of Austria, Bradley said: "I feel like I've improved massively, I've been listening to the coaches like Pep, just taking loads off them in different ways tactically and stuff like that.
"I just want to stay here as long as I can and keep improving, which is the best thing for me.
"It's my first pre-season so it's been quite hard to get used to but I've enjoyed every minute of it. It's hard but it's good."
