Novak Djokovic shows his resilience to beat Alexander Zverev and reach Australian Open semi-finals

World No 1 again comes through the pain barrier and fights back from losing first set in Melbourne

Novak Djokovic celebrates after beating Alexander Zverev in four sets in the Australian Open quarter-final on February 16. AFP

Serbia's Novak Djokovic hits a backhand return to Alexander Zverev of Germany in Melbourne. PA

Alexander Zverev shows his frustration during his defeat to Novak Djokovic. Reuters

Alexander Zverev hits a forehand at Melbourne Park. AP

Novak Djokovic serves to Alexander Zverev during their quarter-final match. AP

Alexander Zverev during his match against Novak Djokovic. AFP

Novak Djokovic hits a return against Alexander Zverev. AFP

Alexander Zverev hits a return against Novak Djokovic. AFP

Novak Djokovic hits a back-hand return against Alexander Zverev. AFP

Alexander Zverev hits a hotdog return against Novak Djokovic. AFP

Novak Djokovic after winning a point against Alexander Zverev. AP

Novak Djokovic continued his successful battle through the pain barrier with victory over Alexander Zverev to reach the semi-finals of the Australian Open.

The world No 1's hopes of a ninth title in Melbourne Park have hung firmly in the balance since he sustained an abdominal injury during his third-round win against Taylor Fritz.

After somehow winning a fifth set in that one, he struggled to a four-set victory over Milos Raonic in Round 4 and he was forced to dig deep into his well of competitive fire to pull out a 6-7, 6-2, 6-4, 7-6 success against Zverev.

"With these type of conditions I need to warm up and I still felt it would take time to feel I could rotate well. It was a close tie break [in the first set] and after that I felt I moved better," said Djokovic.

"I hit slightly more aces, which is a miracle for me. Down to the last shot, it was anyone's match.

"A lot of nerves out there, a lot of pressure. Emotionally, I feel a little bit drained. It was a great battle. We pushed each other to the limit."

As for his ongoing injury problems, the eight-time Melbourne champion added:

"I have suffered injuries at Grand Slams and retired several times, once at Wimbledon in the quarter-finals and the US Open fourth round. The magic hands of my physio, my team and the ATP physios have helped me.

"I've not been practising in the days' off and I will keep doing the same thing and hope the result will be the same."

Germany's Zverev will rue allowing Djokovic back from 4-1 down in the third set and he was also up 3-0 in the fourth.

Djokovic again wore tape on his abdominal area, but it did not appear to bother him as he reached his 39th Grand Slam semi-final, where he will face an unlikely opponent in Russian qualifier Aslan Karatsev on Thursday.

Karatsev, ranked 114th in the world, is the first man in the Open era to reach the last four on his Grand Slam debut.

"To be honest, I hadn't seen him play before this Australian Open but now I've seen him," said Djokovic of the 27-year-old, who beat Grigor Dimitrov 2-6, 6-4, 6-1, 6-2 to reach the last four.

"He's a very strong guy, physical, moves well and has a lot of firepower from the back of the court. He has a great backhand, serves well and has nothing to lose."