Shelton, bidding to reach his first major final, made a confident start by breaking Sinner in the first game of the match - but that was an advantage the 21st seed surrendered three games later after a series of unforced errors.

Shelton, 22, broke again for a 6-5 lead and served for the set but squandered two set points as Sinner dug in to force a tie-break.

Sinner took control from then on, reeling off five straight points to close out the breaker before quickly going up a double break of serve in the second.

The daunting prospect of needing to come back from two sets down against the top seed did not discourage Shelton from entertaining and engaging the crowd.

The American reset admirably to force three break points early in the third set. But, after they went untaken, Sinner struck what proved to be the decisive blow in game five to extinguish Shelton's hopes of an unlikely fightback.

Despite appearing to limp following an awkward landing, Sinner closed out five straight games to secure victory in two hours 36 minutes.

"There was a lot of tension and I had some slight cramps," Sinner said afterwards.

"These matches can go very long. Three sets in two-and-a-half hours is quite some time, so I'm happy to finish it in three."

Sinner's Australian Open title defence comes against the backdrop of his ongoing doping case, which will be heard at the Court of Arbitration for Sport from 16 April, with the World Anti-Doping Agency seeking a ban of between one and two years.