The Italian second seed romped to a 6-1, 6-4, 6-2 victory in just one hour and 49 minutes against the shell-shocked wildcard on Rod Laver Arena.
"Every match is very difficult, so very happy to be in the next round. Very happy with my performance," Sinner said in his on-court interview.
Addressing the crowd, he said: "You have been very fair to me, so thank you very much for the support.
"I feel I am in good shape at the moment," he added. "The body feels good and the mind is in a good moment.
"This is a very special court and very special tournament for me."
The 34-year-old Duckworth was outclassed from the off, with Sinner ploughing through a one-sided first set in just 26 minutes.
Ranked 88 in the world, journeyman Duckworth made a better fist of it in the second set in taking a 2-1 lead as they stayed on serve.
Duckworth grimly held when under severe pressure on his serve but buckled in the seventh game as the 24-year-old Sinner upped the ante.
Any semblance of resistance from Duckworth was broken and it was just a matter of time after that.
Sinner's chief rivals, world number one Carlos Alcaraz and 10-time Australian Open champion Djokovic, had already sealed their places in the third round.
Sinner plays big-serving Eliot Spizzirri, the 85th-ranked American, next as he pursues a Melbourne Park hat-trick.
Should he win three titles in a row in Melbourne, he would join Djokovic as the only men in the Open era (since 1968) to do so.