Melbourne: Novak Djokovic said mental toughness at key moments sets tennis's "Big Four" apart after he subdued battling veteran Lleyton Hewitt to keep his Australian Open title defence on track.
The Serbian world number one joined second seed Rafael Nadal, four-time winner Roger Federer and Andy Murray in the quarter-finals after putting out Australia's last hope in a thrilling contest on Rod Laver Arena.
It is the first time since 1983 that the top five men's seeds have all reached the quarter-finals.
But Djokovic was tested by the grizzled Hewitt, who looked down and out at two sets down and 0-3 in the third before he fought back to seize the third set.
However, the Serb recovered his poise to wrap it up in the early hours of Tuesday, Afterwards he said staying calm at difficult moments was what made the big four so dominant.
"I think it's just the experience that you get playing on the tour that you can use in the certain moments when you feel you are under pressure," said Djokovic, 24.
"And just being able to overcome that pressure with that mental strength, you know, your skills and physical ability as well."
Djokovic, who next faces fifth seed David Ferrer of Spain, said standards in tennis had improved "tremendously" in recent decades.
"Nowadays it's very physical so you have to work very hard, you have to be dedicated, you have to take care of the smallest details off the court as well, how you organise your life," he said. "You have to be emotionally balanced."
Djokovic, who enjoyed a stellar season in 2011 with three grand slam wins, admitted he would face increased expectations and pressure as a result of being world number one, a position he has now held for six months.
"I think physically, mentally I'm motivated, physically I'm fresh, I'm very well prepared. I'm playing really good tennis. Even tonight I played for most of the match a great game," he said.
"I cannot underestimate any opponent. You know, I have to stay dedicated and stay focused. As long as it's like that, I think I'm on the right path," he added.
Meanwhile Hewitt, an ex-number one who needed a wildcard to play in Melbourne, received glowing praise for his fighting performance after looking down and out in the third set.
"Lleyton Brave But Beaten" said the headline in the Herald Sun while The Age said he drew on "reserves that harked back to his glory days". He was the last Australian singles player standing after Bernard Tomic's loss to Roger Federer.
An upbeat Hewitt, who has been plagued by injury problems in recent years, slipping to 181 in the rankings, drew satisfaction from troubling the world number one, who won three grand slam titles last year.
"It was obviously satisfying because he was playing exceptional tennis. I was still able to find a way to get back in the match in some regards, at least put some pressure on him," Hewitt said.