Jannik Sinner admitted he felt “very, very tight” against fellow Italian star Luciano Darderi on Monday night in a sign the scorching Melbourne heat is starting to take a toll.

The two-time Australian Open champion advanced to the quarter finals in straight sets, defeating his countryman 6-1, 6-3, 7-6(2) on Margaret Court Arena.

Sinner raced ahead early on against Darderi, who was clearly feeling the effects of playing against one of the world’s best players on a big stage.

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The world No.25 was lucky to avoid a code violation when he smashed his racquet and then launched a ball into the crowd in frustration early in the second set.

“He needs to be careful here,” Colin Fleming said in commentary for Nine.

Darderi managed to regain his composure in the third set and pushed Sinner to his limits, forcing a tiebreak before getting outclassed when it mattered most.

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Speaking post-match, Sinner admitted it was tricky to navigate playing against a close mate in a grand slam, but he was glad to get the job done in straight-sets with plenty of major matches left on the horizon at Melbourne Park.

“It was very difficult – we are good friends off the court,” he said.

“It felt like in the third set, I had a couple of break chances and couldn’t use them. I got very, very tight, so I’m glad that I closed it in three sets.

“I tried to raise my level, I started off very well in the match and also how I closed with some important pressure points.”

Jannik Sinner defeated Luciano Darderi in straight sets. Getty

Sinner finished with 19 aces, breaking his previous career-best of 17 that he set on Friday in a clinical win over Eliot Spizzirri.

Asked by courtside interviewer Ryan Harrison if it was a conscious effort to finish points quickly, Sinner recognised that the work behind the scenes was paying off.

“I wish it would be that easy,” he said with a smile.

“We put a lot of work in, especially with the serve. I feel a little bit more confident and I feel like there’s still room to improve, which is normal.”

Sinner will face the winner of Ben Shelton and Casper Ruud in the quarter finals.