No. 4 seed Jannik Sinner of Italy will face fifth-seed Andrey Rublev of Russia in the Australian Open quarter-finals. 

Jannik Sinner leads 4-2 in their head-to-head series. However, it's worth mentioning that the Italian was forced to retire in each of his two defeats against Rublev. 

First, Jannik Sinner retired in the first set of his first-ever meeting with Andrey Rublev at the Vienna Open in 2020 as the Russian went on to win the title. The Italian also withdrew during the third set (at 1-1) of their only previous Grand Slam meeting at the 2022 French Open. 

Three years after their first meeting, the pair once again met in the Austrian capital last October. Sinner earned his second win of the season against Rublev in the Vienna Open semi-finals as he also won the title. 

The winner will advance to face either 12^th seed Taylor Fritz of the United States or top-seed Novak Djokovic in the semi-finals. 

Having reached his maiden Grand Slam semi-final at the Wimbledon Championships last year, Jannik Sinner is now bidding to build on his best Australian Open performance. The Italian already reached the quarter-finals once (in 2022), when he lost in straight sets to Stefanos Tsitsipas. 

The Italian continued his impressive Australian Open campaign with a 6-4, 7-5, 6-3 win over Karen Khachanov of Russia in two hours and 35 minutes at Margaret Court Arena.

Jannik Sinner's significant improvement and showcased maturity were more evident during the later part of 2023. It propelled him next to players like Carlos Alcaraz and Daniil Medvedev, who have already won Major titles and managed to beat Djokovic. 

The 22-year-old dominated the likes of Marc Polmans and Casper Ruud in his initial appearances for 2024 at The Kooyong Classic (an exhibition event) in Melbourne. 

Sinner now stands out as the sole quarterfinalist who has not dropped a set at Melbourne Park and could be considered a strong title contender for the season's opening Grand Slam. 

The Italian made significant strides during the latter part of 2023 as he claimed successive victories over Carlos Alcaraz and Daniil Medvedev to eventually win the China Open crown. 

All in all, Sinner played seven ATP finals in 2023 - as much as he did earlier in his career - winning four of them. He lost back-to-back finals to Daniil Medvedev in Rotterdam and Miami, but he had beaten him twice in the final weeks of the campaign - in ATP 500 finals at Beijing and Vienna. 

Sinner also reached the final of the ATP Finals in November, where he lost to Novak Djokovic, but he managed to beat the Serb twice in their three matches last November. 

In August, Jannik Sinner also clinched his maiden Masters 1000 crown at the Canadian Open.

The 26-year-old Russian has undergone a notable transformation in the mental aspect of his game over the past year or so. Rublev already possesses a strong self-belief in his ability to navigate challenging moments in matches against players who may not fall into the elite category. 

This evolved mental resilience has been evident multiple times since the start of the new season, contributing to Rublev's 15^th ATP title in Hong Kong and guiding him to the quarterfinals at Melbourne Park.

Rublev overcame a considerable challenge against Thiago Seyboth Wild of Brazil in the first round and narrowly edged the in-form home favorite Alex de Minaur in the last-16, though the Australian won back-to-back tiebreaks. Yet, the Russian outlasted De Minaur in a thrilling five-setter at Rod Laver Arena that lasted four hours and 15 minutes. 

The next challenge for Andrey Rublev now is to demonstrate this mental resilience against top opponents in Grand Slams - something he's yet to accomplish. Despite his 15 tour-level titles, including a Masters 1000 title at Monte Carlo last year, the Russian has been unable to progress beyond the quarterfinals in Major tournaments up to this point. 

Moreover, the world No. 5 is yet to win a Grand Slam quarter final in nine attempts. Seven of these defeats were against superior players, though, including three encounters with his fellow compatriot Daniil Medvedev, as well as Novak Djokovic (twice), Rafael Nadal and Stefanos Tsitsipas. 

Jannik Sinner is currently playing at a different level compared to the rest of the tour, and he deserves to head into this quarterfinal as the overwhelming favorite, but it won't be an easy match for him. Both players have shown great development in the past season and we expect a tight battle between them at Rod Laver Arena.