MELBOURNE: Serbia's Novak Djokovic celebrates after winning against Germany's Alexander Zverev during their men's singles quarter-final match on day nine of the Australian Open tennis tournament in Melbourne yesterday. - AFP

MELBOURNE: Eight-time winner Novak Djokovic smashed his racquet en route to a tense, four-set win over Germany's Alexander Zverev to reach his 39th Grand Slam semi-final at the Australian Open yesterday. It was a patchy performance from the world number one, who is nursing an abdominal injury and drew deeply on his mental fortitude to win 6-7 (6/8), 6-2, 6-4, 7-6 (8/6).

"With this condition (injury), I need time to warm up and actually feel like I can rotate well," said Djokovic, who started sluggishly but finished with 23 aces and 48 winners, along with 56 unforced errors. "I started moving better and playing better. I served extremely well and I think I had slightly more aces than him, which for me is a miracle. "There were a lot of nerves out there and I feel emotionally a bit drained. "I kind of regained my focus after I broke that racquet and things started to shift to me in a positive direction."

Djokovic will be hot favorite to advance to Sunday's final when he plays Russian qualifier Aslan Karatsev, who continued his dream run with a 2-6, 6-4, 6-1, 6-2 win against injured Bulgarian Grigor Dimitrov. "I hadn't seen him play before the Australian Open," he said of 114th ranked Karatsev. "He's very physically strong and moves well. He has a lot of firepower from the back of the court. "He's motivated and has nothing to lose."

The Serb remains on track for a record-extending ninth Australian Open title and 18th Grand Slam trophy, nipping at the heels of rivals Roger Federer and Rafael Nadal, who both have 20. Djokovic and Zverev went the distance in a see-saw clash in the warm-up ATP Cup, foreshadowing what was ahead. Having played three straight grueling matches, a lethargic Djokovic dropped his opening service game and labored through the first set, which Zverev claimed in a tense tiebreaker to take the early lead. Djokovic's impenetrable game returned in a dominant second set marked by sliding retrievals and unrelenting punching from the baseline.

But Djokovic couldn't continue the momentum in the third set and his frustration boiled over when he was unable to crack Zverev's serve, as he smashed his racquet three times on the court. Djokovic, however, regrouped and gained a stranglehold by pulling off five straight games to edge ahead. The twists continued in the fourth set with Zverev running out to a 3-0 lead until Djokovic once again hit back.

He proved nerveless in the decisive tiebreaker, finishing it off with an ace to clinch his 19th straight win at the Australian Open. Djokovic last tasted defeat in the fourth round in 2018, when he was upset by unseeded Hyeon Chung of South Korea. Zverev, who served 21 aces, lost to Dominic Thiem in last year's Melbourne semis, and fell agonizingly short against the Austrian in his only Grand Slam final at last year's US Open.

Semi-final showdown

Earlier yesterday, Serena Williams blasted past Simona Halep to set up an Australian Open semi-final showdown with Naomi Osaka, as Russian qualifier Aslan Karatsev extended his fairytale run. Williams took a step towards a record-equaling 24th Grand Slam title with a 6-3, 6-3 dismantling of second seed Halep, the American's nemesis in the 2019 Wimbledon final.

Williams, 39, said her level was improving ahead of her meeting with Japan's Osaka, who came out on top in their tempestuous 2018 US Open title match. "Definitely think this is the best match I have played this tournament, for sure," said the 10th seed. "Obviously I had to, going up against the number two in the world, so I knew I had to do better."

Their semi-final promises much after Osaka, the reigning US Open champion, looked in great touch in her 6-2, 6-2 win over Taiwan's Hsieh Su-wei. Displaying great focus against the awkward Hsieh, ranked 71 and playing her first Slam quarter-final aged 35, Osaka hit 24 winners and was detained on Rod Laver Arena for only 66 minutes. "I told myself just to be really intense from the beginning," said the Japanese star, the reigning US Open champion. I felt like I knew what to expect and that I couldn't afford to be lazy with my footwork or anything."

Elsewhere, 114th-ranked Karatsev became the first man to reach a Grand Slam semi on debut when he ousted a hobbling Grigor Dimitrov 2-6, 6-4, 6-1, 6-2. The 27-year-old has knocked out three seeds on his run to the last four, where he will face world number one Novak Djokovic. "It's an unbelievable feeling," said Karatsev, whose career so far has been badly compromised by injury. "It was tough at the beginning for me to hold my nerves, but I tried to find a way to play."

Karatsev becomes only the second qualifier to reach the Australian Open semi-finals after Bob Giltinan in 1977. He is also the lowest-ranked man to make the semis at a Slam since 125th-ranked Goran Ivanisevic at Wimbledon in 2001. After a five-setter with Felix Auger-Aliassime in round four, Karatsev had an easier ride against Dimitrov who was wincing with pain from the third set. The Bulgarian 18th seed, who was barely able to serve because of back spasms, took a medical timeout, but his movement was always hampered and he limped off the court after Karatsev's win. - AFP