Compared to Roger Federer's best effort of 23 straight grand slam semi-finals, which ended at the French Open in 2010, Novak Djokovic reaching the last four of a major for the 11th consecutive time might not seem that impressive an achievement.

Yet when you consider that Djokovic has achieved his tally in an era when Rafael Nadal – when fit – Federer and Andy Murray have been pushing him all the way, it is a remarkable statistic.

A pedant might point out that the Serb does not have to play any of his top-four rivals until that point but it is testament to his consistency, both physical and mental, that Djokovic finds himself in yet another semi-final, back at the Australian Open where he won his first slam title in 2008 and was crowned champion again in 2011 and last year.

As Murray prepared to face the unseeded Frenchman Jeremy Chardy in his quarter-final in the early hours of this morning, UK time, the world No.1 was once again demonstrating his powers of recovery and mental strength as he saw off Tomas Berdych 6-1, 4-6, 6-1, 6-4.

Beating the in-form Czech, the fifth seed, is no mean feat when you are fully rested and able to give 100% from the start; when you have come off a fourth-round match that lasted five hours and two minutes, being as fresh as Djokovic was yesterday was little short of remarkable.

In this post-Lance Armstrong confessional era, such resilience invites raised eyebrows but Djokovic said he was "doing everything legal" to recover between matches. "People who don't know tennis, who have never been in those kinds of situations, would not truly understand what the player has to go through, not just when you prepare for a grand slam, but also during a grand slam," Djokovic said after an encounter with Berdych that lasted just over two and a half hours.

"After five hours of a match, you need to really put a lot of time into recovery, different kind of recoveries. I understand that many people have many different views and opinions and I respect that. But I'm doing everything in my power that is legal, correct, and natural, and it's working well."

Given what he had to go through against Stanislas Wawrinka in the previous round, it looked as if Djokovic was trying to get things done as quickly as possible as he romped through the first set. Berdych has all the power in the world but it wasn't until the second set that he found the opportunity to use it. A break in the first game put him on his way and he retained the advantage throughout to level the match at one set apiece.

That might have been the encouragement Berdych needed to push on and drain Djokovic's energy but instead the defending champion stormed out of the blocks in the third set to lead 3-0 and never looked back, taking the set with ease. He broke for 2-1 in the fourth and, although Berdych battled hard, stayed strong and held serve to clinch victory and a match-up with David Ferrer.

Berdych said he felt Djokovic was the fittest player on the tour. The Serb said an enormous amount of work goes into getting him ready. "I consider myself fit [but] I have a great team of people around me who are using their expertise to make me feel ready – physically, mentally, emotionally – for every match, every challenge.

"Obviously, it's not easy to always be at 100% fitness, but after a five-hour match two days ago against Stan, I was quite convinced I could recover for this one. The team did a great job."

Early in his career, even when he was ranked No.3, Djokovic had a reputation for retiring in matches, often because of breathing difficulties. A sinus operation at the end of 2007 helped a lot, with his first grand slam title following soon afterwards. A gluten-free diet and change in routine added to his physical strength, while Djokovic said experience also helped.

"At the start of my career I went through a lot of different kinds of challenges, physically, mentally," he said. "Everybody makes mistakes. I was aware of the fact that I needed to improve because I wasn't feeling well, especially in the heat. I had lots of health issues.

"Maybe that's one of the reasons why I'm being so cautious and so committed when it comes to recovery because I've had those experiences, bad experiences, before in my career and I know what it feels like. I don't want to go through it again. I am aware of the importance of practice and recovery on a daily basis."

Djokovic's semi-final is likely to be another survival of the fittest. Ferrer recovered from two sets down to beat his fellow Spaniard Nicolas Almagro 4-6, 4-6, 7-5, 7-6, 6-2. Almagro served for the match once in the third set and twice in the fourth, with his failure to finish the job allowing the indefatigable Ferrer to hit back for a victory he described as "a miracle". He has never been to a grand slam final and he might need another miracle if he is to reach this one.