Defending champion Novak Djokovic will face another test of his extraordinary fitness when he takes on Spanish terrier David Ferrer for a place in the Australian Open final on Thursday.
The Serbian world number one has looked the player to beat so far with an epic five-set, five-hour victory over Stanislas Wawrinka and an untroubled dismissal of fifth seed Tomas Berdych in the quarter-finals.
Now comes a war of attrition with the relentless Ferrer, whose never-say-die attitude will again test Djokovic's stamina in an expected long, drawn-out night semi-final on Rod Laver Arena.
Ferrer, the fourth seed in Melbourne this year in the absence of celebrated countryman Rafael Nadal, modestly baulks at talk that he belongs to the exclusive group alongside Djokovic, Roger Federer and Andy Murray.
He declares Djokovic is the best, raising questions about whether he has the self-belief that he can deny the top seed his expected place in Sunday's final.
"Nole (Djokovic), he's a special player. He has all the shots. He's the best, I think," said Ferrer, 30.
Ferrer added that he remains a step behind the game's 'Big Four' despite being poised to overtake long-time injury absentee Nadal in the rankings next week.
"I am top four because Rafael has been injured a long time. It's true," Ferrer admitted.
"I think the top four, they are better. It's my opinion. But I am trying to win every match. The results, are there, no? I'm not making something up.
"It's very difficult for me to win a Grand Slam because there are the top four. At this time they are better than the other players."
Djokovic, who has confirmed his number one ranking by reaching the semi-finals, has beaten the Spaniard twice in the Melbourne quarter-finals and twice in the US Open semis, and is the favourite again on Thursday.
"I need to be aggressive on the court, that's for sure," said Djokovic, who is hoping to his fourth Australian Open final in six years.
"I need to step in and try to be in control of the match, otherwise he makes his own rhythm, he makes his own pace on the court. That's where he's very dangerous.
"He's a great competitor. He's somebody that has a lot of respect from all the players because he's playing so many tournaments and works very, very hard.
"You can see because he's in his 30s and one of the fittest players around and is playing the best tennis of his life in the last 15 months. It's the semis of a Grand Slam, so I expect a tough match."
Djokovic again underlined his bottomless stamina reserves with his recovery from the fourth longest match on record at the Australian Open against Wawrinka by bouncing back to dominate Berdych.
Last year he bested one of the fittest players on tour when he edged out Nadal in the 5hr 53min final, the longest-ever match at Melbourne Park, just two days after seeing off Murray in a five-set semi-final over 4hr 50min.
While Djokovic agrees that the top four have dominated men's tennis, scooping up all of the last 12 Grand Slams since Juan Martin Del Potro's 2009 US Open win, he is wary that Ferrer could break through.
"You rank the top players as favorites and main contenders to win the title, but you can never rule out the second group from five to 10," he said.
"Del Potro, (Jo-Wilfried) Tsonga, Berdych, Ferrer, those are the guys that can surprise, that have proven on several occasions they can win against top players.
"There has been a certain domination in the last few years from the top four (but) we can never underestimate the quality of the rest of players, so it can happen any time."