Sinner sent down 19 aces to march into the quarter-finals with a 6-1 6-3 7-6 (7-2) win over fellow Italian Luciano Darderi at Margaret Court Arena on Monday night.
It was the highest single-match tally of aces in the four-time major champion's career, an improvement on the 18 he fired in a second-round Open win over local James Duckworth.
"We put a lot of work in, especially with the serve," Sinner said.
"We changed a bit in motion and I feel for sure a little bit more confident.
"I feel like there's still room to improve, which is normal, but I'm very happy with how I've come back in the new season.
"Because at the end of (last) season I served very well, but now it's for sure a bit more stable."
Now on an 18-match winning streak at Melbourne Park, Sinner looked firmly in control during the first two sets against Darderi, who required treatment on a left quadriceps injury before the third set.
But the world No.2 was made to dig deep and vary his tactics in order to seal the result as his countryman refused to lie down.
"I try to go a bit more to the net and being slightly more unpredictable, which today I think worked really, really well," Sinner said.
"Now let's see what's coming."
What's coming is American eighth seed Ben Shelton who defeated 12th-seeded Norwegian Casper Ruud 3-6 6-4 6-3 6-4.
Shelton has lost eight straight against Sinner including in last year's semi-finals at Melbourne, but said he was up for the fight.
"I wanted to be back here, give myself another shot, improve on some things I didn't do last year, leave it all out on the court. I have lot more I want to do here, a lot more I want to improve."
Left-hander Shelton has a powerful serve himself, setting up three match points with a 228 kph ace, and clinching the game at the first attempt with a crosscourt forehand.
In contrast to his four-set battle with Eliot Spizzirri, in which he cramped and looked in huge bother under extreme heat, Sinner was in control from the outset against Darderi.
He breezed through the first set and while Darderi made a more aggressive start to the second, the underdog quickly lost his way.
Darderi smashed a racquet and copped a code violation for ball abuse, blowing up after dropping the third game of the second set on serve.
The 23-year-old then required treatment on his injury and it looked as if Sinner would cruise to victory over his hobbled opponent.
But Darderi showed fight and Sinner had to survive four break points at 4-4 in the third set, before sealing the match in a tiebreak.
He was 0-2 down in the tiebreak before rattling off seven straight points.
"It was very, very difficult," Sinner said.
"First of all, we are good friends off the court. It's also that difficulty to also put away.
"I'm very happy that I closed it in three sets.
"I tried to raise my level. I started off very well the match and also how I closed with some really important pressure points."
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