MELBOURNE (Reuters) - Reigning champion Novak Djokovic overcame several dips in form to beat Alexander Zverev 6-7(6) 6-2 6-4 7-6(6) and book his place in the Australian Open semi-finals on Tuesday.
The Serbian world number one hit back strongly after losing a tight opening set on a tiebreak but trailed in both the third and fourth sets before turning them around.
German sixth seed 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, a legacy of the injury picked up in his third-round win over Taylor Fritz. 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.
"After the tiebreak I felt like I started moving better, I started serving better and ended up with more aces than him which is a miracle against someone like Sacha," Djokovic, whose route to the semi-finals has been a struggle, said.
"There were lots of nerves out there, emotionally I feel a little drained, it was a great battle, tough luck to Sacha. We pushed ourselves to the limits."
The 23-year-old Zverev began in confident fashion and broke Djokovic's opening service game as the favourite initially struggled to get into his usual silky rhythm.
Zverev failed to convert a set point on Djokovic's serve when leading 5-3 and wavered on his own serve at 5-4 but showed plenty of composure as he edged the opening tiebreaker when Djokovic fended a return long.
While the first set took an hour, Djokovic needed only 29 minutes to grab the second as Zverev lapsed.
An unpredictable match them took another change of direction as Djokovic went off the boil and Zverev moved into a 4-1 lead, with the Serb's frustration boiling over as he destroyed a racket, leaving fragments of frame across the baseline.
Zverev was 0-30 ahead on Djokovic's serve in the next game but Djokovic clicked back into gear, reeling off 20 of the next 24 points to move one set from victory.
Again Zverev forged ahead in the fourth set and he had three points to move into a 4-0 lead but Djokovic hung on.
Djokovic, bidding for a record-extending ninth Australian Open title, chiselled his way back into a high-quality set, saving yet another break point at 3-4.
Zverev was happy to trade from the baseline in long exchanges and a sumptuous backhand winner earned him a set point in the 12th game, only for Djokovic to reply with an ace.
Djokovic squandered his first match point in the tiebreak with a sliced backhand into the net but a dipping backhand earned him a second opportunity, this time on his own serve, and his 23rd ace sealed victory.
With 114th-ranked Karatsev up next, it would be a huge surprise if Djokovic is not contesting Sunday's final. But he said he will not be taking the Russian lightly.
"To be honest I hadn't seen him play before this Australian Open but now I've seen him," he said.
"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."
(Reporting by Martyn Herman; Editing by Hugh Lawson)