MELBOURNE: Rafael Nadal knows he must find a way to defuse the booming serve of Milos Raonic on Wednesday if he is to stay on course for a dream Australian Open final with Roger Federer.

The chances of a ninth Grand Slam final between the old rivals have dramatically improved after the shock exits of top seeds Andy Murray and Novak Djokovic put the title up for grabs.

But 30-year-old Nadal, the 14-time Grand Slam champion, first has to get past third seed Raonic, the highest-ranked player still standing in the men's quarter-finals.

The Canadian, yet to win his first major title, suffered heartbreak in last year's Melbourne semi-finals when a groin injury put paid to his chances against Murray.

But he should pose Nadal his biggest problem yet in this year's tournament, where the Spaniard is bidding to end a major title drought stretching back to the 2014 French Open.

The winner will face either Bulgaria's Grigor Dimitrov or Belgian David Goffin in the semi-final in the bottom half of the draw.

Nadal leads Raonic 6-2 in their meetings, but he lost to the power-server only this month, over three sets in the Brisbane International quarter-finals.

"He's an opponent that makes you feel you're playing with a lot of pressure all the time because his serve is huge and he's playing very aggressive from the baseline," Nadal said.

"So it's going to be a very tough match and I need to be very focused with my serve and play aggressive. If I am not playing aggressive, then I am dead."

Nadal has shown his trademark fighting qualities in reaching his first Slam quarter-final in 18 months after a series of injuries.

After overcoming top-rated German teenager Alexander Zverev over five sets in the third round, he also needed four sets to subdue flamboyant Frenchman Gael Monfils on Monday.

Aces high

Raonic, who is working with Dutch Wimbledon champion Richard Krajicek, has served 93 aces in the tournament so far, second only to 6ft 11ins (2.11m) Croatian Ivo Karlovic.

The Canadian, who has been suffering from 'flu, cracked 33 aces in overcoming Spaniard Roberto Bautista Agut in the fourth round after struggling early in the match.

Looking back on his recent win over Nadal in Brisbane, Raonic said: "We both tried to be the aggressors early on. I fought through a difficult moment midway through that second set.

"Then, I thought I had it pretty handily after that point. I broke towards the end of that second set. Broke right away in the third.

"Obviously it's very within me to find those solutions again."

Dimitrov, who will be playing in his third Grand Slam quarter-final, downed Goffin in their only meeting in the third round at the 2014 US Open.

The Bulgarian 15th seed lost to Nadal in the quarter-finals in Melbourne three years ago and reached the semi-finals at Wimbledon in 2014, where he lost to Djokovic.

"David is an excellent player. I know what to expect from him. We've practised against each other a few times this off-season," Dimitrov said.

"He's been serving really well and has served his way out of trouble. It's one of his biggest weapons and he's one of the greatest defenders out there."

Goffin became the first Belgian man to reach the Australian Open quarter-finals when he knocked out eighth seed Dominic Thiem over four sets in intense heat.

"I'm feeling more confident against the top players. I've had a lot of matches before the tournament," Goffin said.

-AFP