By SABC Sport
14th October 2023
The 20-year-old defender played the whole game as England ran out 1-0 victors at Wembley, making the step up from winning the European Under-21 Championship in the summer.
Having spent last season on loan at Brighton, Colwill has started all eight of Chelsea's Premier League games so far this term.
He earned a first senior call-up from Gareth Southgate last month but had to wait until Friday's friendly against the Socceroos to make his bow.
"It was amazing," he told beIN Sports.
"(A win and a clean sheet is) the best way to have a debut and hopefully we can build off the performance against Italy as a team and individuals and go from there."
Having progressed through the ranks for both club and country as primarily a centre-back, Colwill started on the left of defence against Australia and has also operated there for Chelsea in recent weeks.
"Obviously, it is a different role," he said.
"But I have been playing there for my club and I am enjoying it and if it gives me a chance to start and to play, I'm all for it."
Southgate made 10 changes for the game as a blend of fringe players and young talent was given the chance to stake a claim.
The England manager admitted afterwards that he had given his team a "difficult task" as a lack of "cohesion" made for a tougher evening than he would have liked.
"We have had a few days, we met on Monday so we have been training hard," Colwill added on the unfamiliar look to the team.
"Getting to know players is obviously tough as that isn't a lot of time but I think we put in a performance we can be proud of and we have just got to build from there."