After Novak Djokovic completed a grueling four-set win in the fourth round of the Australian Open in the early hours of Tuesday morning, the Serbian stepped back on the court to speak with former World No. 1 and on-court interviewer Jim Courier. The American asked how Djokovic was holding up after a physical battle against Daniil Medvedev.

“Since I guess my next opponent is watching, I’m feeling fantastic. I’ve never felt fresher in my life,” he said.

Djokovic was joking. But he’ll certainly hope he feels fresh, because another tough test looms in the quarter-finals. The top seed faces Japanese superstar Kei Nishikori, who triumphed in a fifth-set tie-break in the fourth round, on Wednesday with a spot in the last four on the line.

“Kei won another marathon match. Congratulations to him for fighting back from two-sets-to-love down and a break down,” Djokovic said. “He’s a fighter. He’s a very talented player. One of the quickest players on the Tour. I have lots of respect for him.”

Nishikori’s victory against Pablo Carreno Busta was not his first marathon at Melbourne Park this year. The eighth seed rallied from two sets down in the opening round, and then outlasted 39-year-old Ivo Karlovic in a fifth-set tie-break in the second round. Time and time again Nishikori has been tested this fortnight, but despite spending 13 hours and 47 minutes on court — that total leads the four players in the top half of the draw and is three hours and 22 minutes more than second seed Rafael Nadal has spent in action advancing to the semi-finals — he has kept on winning, and that’s what counts.

“I’m really glad how I came back,” Nishikori said after overcoming a 5/8 deficit in his final-set tie-break against Carreno Busta. “I don’t even know how I come back, but [I’m] very happy to win.”

Another obstacle he’ll have to overcome is what has been a lopsided FedEx ATP Head2Head rivalry with Djokovic. The six-time Australian Open champion, who is trying to separate himself from Roger Federer and Roy Emerson by winning a record seventh trophy at the tournament, has won 15 of their 17 clashes, including 14 in a row.

“Every year is different, so every match that you play against each other is different, so I expect him obviously to come out, to try something new,” Djokovic said. “I have beaten him many times that we played against each other in the past couple of years and we played on different surfaces. [There were] a couple of very close matches. I expect a tough one.”

The winner of that battle will face either former World No. 3 Milos Raonic or 28th seed Lucas Pouille. While Raonic advanced to the semi-finals in Melbourne just three years ago, Pouille had not won a match at the season’s first Grand Slam before this edition of the event.

“We worked very hard during the pre-season and during the beginning of the year, so I think that, as we say, hard work pays off,” Pouille said. “The tournament is not over, but I’m very happy to be here now and I’m going to be focused on the next match tomorrow to try to reach my first semi-final. It will be great.”

Perhaps nobody has faced a more difficult road to this stage of the tournament than Raonic. In the first round, he had to play talented Aussie Nick Kyrgios, and then 2014 champion Stan Wawrinka in the second round. The Canadian ousted reigning Nitto ATP Finals titlist Alexander Zverev in the fourth round to set his match against Pouille.

“It’s not fun necessarily before the tournament starts to look at it and say, ‘hey, you play Nick to most likely play Stan in the first two rounds.’ You’re sort of hoping for a bit more time to really work your way into things,” Raonic said. “But then on the other end of it I dealt with those challenges really well. Right now I’m here playing some extremely good tennis, I believe. Hopefully I can make that count.”

Pouille will face a challenge in trying to work his way into Raonic’s service games. The 16th seed Raonic has won 94 per cent of them in his first four matches, facing just five break points in the tournament. He also is the tournament’s co-leader (w/Opelka) in aces with 107. Raonic has won their three previous FedEx ATP Head2Head meetings without dropping a set, and losing serve just once in seven sets.

Pouille arrived in Melbourne having lost five of his past six matches.. But with new coach Amelie Mauresmo by his side, he is set to compete in his third major quarter-final.

Rafael Nadal was business-like and at times ruthless in his victory over Frances Tiafoe on Tuesday night at the Australian Open. The 2009 champion ended the run of the #NextGenATP American 6-3, 6-4, 6-2 in one hour and 47 minutes for a place in his 30th Grand Slam championship semi-final.

The second-seeded Spanish superstar, who is bidding to capture his 18th major crown in his first tournament since September 2018 at the US Open, won 84 per cent of his first service points and struck 29 winners past Tiafoe, who committed 34 unforced errors.

Nadal will next challenge No. 14 seed Stefanos Tsitsipas of Greece for the third time. He leads their FedEx ATP Head2Head series 2-0, with final wins in 2018 on the clay of the Barcelona Open Banc Sabadell and on the hard courts of the Rogers Cup.

Nadal won 14 of the first 17 points — including the first service break in the second game — in an electric start by keeping his groundstroke length consistently deep to push Tiafoe around the court and behind the baseline. At 0-3, Tiafoe slowed down his serve to settle his nerves, and began to work his way into the match, but Nadal went 15 for 15 on first serve and finished the opener with consecutive forehand winners.

From 5-3 up in the first set, Nadal won 12 of the next 13 points to maintain control against Tiafoe, who missed out on two break point chances — due to forehand errors — when his Spanish opponent served at 2-1 in the second set. Tiafoe found his service rhytmn, but at times he rushed and hit closer to the lines. Nadal was simply ruthless in striking anything short for a winner, yet Tiafoe resisted the pressure to save three set points when serving at 3-5. Nadal closed out to love in the next game, finishing with a smash winner from the baseline.

Tiafoe, with a 1-5 record in fifth sets, lost his first service game for the third time to immediately be placed on the back foot in the third set. Three groundstroke errors handed Nadal another break for a 5-2 advantage, before the World No. 2 closed out to 15 with Tiafoe hitting a backhand wide.

Only Roger Federer (43), Novak Djokovic (34), who plays Kei Nishikori in the quarter-finals at Melbourne Park on Wednesday, and Jimmy Connors (31) have reached more major semi-finals than Nadal in the Open Era (since April 1968).

Tiafoe had been bidding to become the youngest American man to reach the semi-finals at the Australian Open since Andy Roddick (20 years, 149 days) in 2003.

It didn’t have the flair or style of his victory against Roger Federer, but Stefanos Tsitsipas’ win against Roberto Bautista Agut showed an entirely different – and maybe more impressive – side of the 20-year-old Greek. Where he wowed the Federer crowd with shake-your-head winners, against Bautista Agut, Tsitsipas showed the hustle and grit it might take for him to win his maiden Grand Slam title this fortnight.

The reigning Next Gen ATP Finals champion reached his first Grand Slam semi-final on Tuesday, ending the ironman run of Spain’s Roberto Bautista Agut 7-5, 4-6, 6-4, 7-6(2) under the baking Melbourne sun.

The Greek was slow to start his first quarter-final and fell behind a break in the first three sets, including a 2-4 deficit in the third. But he returned to his net-charging play that helped him knock out Federer and woke up his cadre of Greek fans, who had been quiet for much of the quarter-final, before controlling the fourth-set tie-break with more aggressive play.

Tsitsipas becomes the youngest man (20 years 168 days) to reach the Australian Open semi-finals since Andy Roddick (20 years 149 days) in 2003 and the youngest man to reach a Grand Slam semi-final since Novak Djokovic (20 years, 110 days) at the 2007 US Open.

Tsitsipas, who had reached only one fourth round at a Slam before this fortnight, set three main goals to start the year: Crack the Top 10 of the ATP Rankings, make the Nitto ATP Finals in November, and reach a Grand Slam semi-final. Three full weeks into the season, and he’s a third of the way there. He will face either 17-time Grand Slam champion Rafael Nadal or #NextGenATP American Frances Tiafoe, who’s playing in his first major quarter-final.

“I’m just living the dream, living what I’ve been working hard for. I mean, I feel a bit emotional but not too much because I know, again, I really worked hard to get here, the semis of a Grand Slam,” Tsitsipas said.

The Greek had to endure a nervy start inside Rod Laver Arena, dumping an overhead into the net to lose his opening service game. Bautista Agut somehow looked the fresher, despite having played three five-set matches out of four to make his first quarter-final.

The 30-year-old was moving Tsitsipas from tramline to tramline and landing passing shots at the 20-year-old’s ankles when the Greek sprinted forward. But Tsitsipas began to probe Bautista Agut’s legs, hitting behind the Spaniard again and again, and he broke in the 12^th game to take the opener.

Another slow start in the second, however, doomed Tsitsipas’ chances, as Bautista Agut never let up and Greece’s #NextGenATP star lacked the precision that helped him knock off his idol on the same court two days earlier.

A five-set match became a three-set match, and Tsitsipas honed in his focus, pounding Bautista Agut’s backhand, making the Spaniard, who was finally showing the effects of his marathon run, stretch with both hands and stay home. Two, three, four consecutive topspin-heavy shots to the backhand, and Tsitsipas would then step in to rip a forehand down the line or race forward for a putaway.

The fourth set was a serving contest until the tie-break, when Tsitsipas, the fresher of the two, had just enough left to take the tie-break and book a spot in the final four.

He might land that Top 10 ATP Ranking he’s chasing this fortnight as well. Tsitsipas is projected to climb to No. 12 and, if he makes the final, he’s projected to enter the Top 10.