Jannik Sinner gives fitness update after setting up blockbuster Novak Djokovic Australian Open clash

"I was struggling. We go day by day," Sinner admitted following his commanding quarter-final triumph.

He credited his previous round victory over compatriot Lorenzo Sonego with providing a psychological lift.

"Today I felt I was moving a little bit better; I felt I recovered physically again," he said, expressing delight at reaching the semi-finals of the season's opening major.

Sinner was full of admiration for Shelton's formidable serve, describing the American as an increasingly difficult opponent who continues to develop his game each season.

"It is very tough to play against Ben. He has a huge, huge serve, and I feel like he is improving so much year after year, especially after the off-season," the defending champion said.

When asked how he manages to return such powerful deliveries, Sinner offered a modest explanation.

"Honestly, I don't know. It's just instinct and not always the power matters," he revealed, noting that Shelton's left-handed delivery presents a rare challenge on tour.

"We don't have many lefties in our game, so it is definitely one of the toughest challenges to return his serve."

Sinner will now face Djokovic after the Serbian progressed in fortunate circumstances when Lorenzo Musetti was forced to retire through injury.

The Italian had been leading two sets to love and appeared on course to eliminate the 24-time Grand Slam champion before an unexpected injury struck, prompting a medical timeout and an emotional withdrawal.

Despite Djokovic's unconvincing route to the last four, Sinner insisted he would approach the contest with full respect for his opponent.

"These are the moments you practice for. You wake up in the morning and look forward to playing a good match," he declared.

"If you want to win, you have to play at your best."

Sinner reflected on the significance of facing Djokovic, acknowledging the valuable lessons he has learned from previous encounters with the veteran.

"Also, in the past, I have had great lessons. It doesn't really matter the result. It improves you as a person," he said, adding: "We are still lucky to have Novak here playing incredible tennis at his age."

The four-time Grand Slam winner expressed hope for an entertaining battle, whilst recognising the immense difficulty ahead.

Regarding the other semi-final between Carlos Alcaraz and Alexander Zverev, Sinner noted that players must focus on their own preparations when competing on the same day.

"It is hopefully going to be a great couple of semi-finals," he concluded.