MELBOURNE (AFP) - Defending champion Novak Djokovic swept past Diego Schwartzman on Sunday (Jan 26) and into an Australian Open quarter-final with big-serving Milos Raonic, as he zeroes in on an eighth Melbourne Park title.

The rampant Serbian second seed was on another level to Schwartzman, the 14th seed, crushing the Argentinian 6-3, 6-4, 6-4 on Rod Laver Arena to book an 11th appearance in the tournament's last eight.

Raonic is his next hurdle and the Canadian has also been in fine touch. He is yet to drop a set, blasting past fellow former world No. 3 Marin Cilic 6-4, 6-3, 7-5.

"Milos is one of the tallest, strongest players on tour and has one of the biggest serves," said Djokovic, who is into his 46th Grand Slam quarter-final, second only to Roger Federer's 57.

"I've got to be ready for missiles coming from his side of the net. One key element will be how well I'm returning."

The Serb has met 32nd seed Raonic nine times and won them all.

But the Canadian is back to full fitness after years of injury struggles and his powerful serve could cause problems. So far he has served 59 games and won them all.

Asked what he needs to do to beat Djokovic, he replied: "I think I'm going to have to hit more than 35 aces," referring to the number he pumped past 2018 finalist Cilic.

"I think we play quite opposite from each other, and he's done a good job in the past neutralising my serve," he added of the Serb.

"So I have really got to focus on my things well and be the one dictating."

Meanwhile, on a personal note, Djokovic says that while his young son is a big tennis fan who likes picking up a racquet, but he will not be pushing him to follow in his footsteps.

The Serbian star has two children with wife Jelena and five-year-old Stefan told his dad he was "born with a backhand".

"Obviously he's exposed to tennis a lot when he travels with me but also on the TV. He knows what is going on. He knows Roger (Federer), he knows Rafa (Nadal)," Djokovic said. "He knows a couple of the other guys. His favourite shot is forehand so far. I'm trying to get him to hit a few backhands. He's been telling me that he is born with a backhand."

The 16-time Grand Slam winner, who began playing the sport aged four and was sent to a Munich tennis academy at 12, said he would not press his children into the sport unless they showed genuine desire. But the ultimate call might come down to his wife.

"I really want him and my daughter (Tara) to express honest desire to take the racquet and the ball and just hit. Go to the court or up against the wall," he said. "I would be more than happy to support them in their tennis careers and journeys but it's still very early to talk about it... my wife says!"

The Australian Open is 1.96m Raonic's favourite Slam.

He reached the semi-finals in 2016, when he lost to Andy Murray, and the quarters on three other occasions, including last year.

His career, though, has been plagued by injuries, with operations over the years for hip, foot and wrist problems. He has also struggled with back, ankle, calf and knee issues.

He said it felt "pretty damn good" to finally be injury free.

Quality player

While Djokovic had won all three of his past meetings against Schwartzman, the Argentinian had caused him problems previously and he needed to come from two sets down at Roland Garros in 2017 to win.

Despite this, the writing was on the wall - Schwartzman had never beaten a top-five player in 21 clashes, and it was not about to change on Sunday.

They went game for game in the opening set until Djokovic pounced, working a break point to get the crucial edge and go 5-3 in front.

Sensing a quick victory, he stormed to a 3-0 lead in the second set, breaking twice.

But Schwartzman is a fighter who runs and scraps for every ball and he pulled back a break, only for the world No. 2 to calmly serve out the set.

The scurrying Argentinian is renowned as one of the fastest men around court and did all he could to claw back into the match, but Djokovic's searing groundstrokes and pinpoint serving gave him few chances and the end quickly came.

"Diego is a quality player and I knew if I gave him time he could do a lot of damage from the back of the court," said Djokovic, seeking to become only the third man to win eight or more titles at the same Grand Slam after Rafael Nadal (12 French Opens) and Roger Federer (eight Wimbledons).

"I tried to mix it up a bit, bringing him from the back of the court with the slice."