Djokovic scrapes into last 8

Novak Djokovic dished up 100 unforced errors in a five-set struggle with Gilles Simon on Sunday as Roger Federer roared into the Australian Open quarter-finals with ruthless efficiency.

After the top seed's "match to forget", Federer looked in a hurry to brush off David Goffin when they came on court just before 11:00 pm -- and he duly thrashed the Belgian 6-2, 6-1, 6-4 in 88 minutes.

There was a big contrast between defending champion Djokovic, who is going for a record-equalling sixth Australian Open title, and the 34-year-old Federer, who hasn't won in Melbourne since 2010.

While Simon patiently pushed and prodded Djokovic during his 6-3, 6-7 (1/7), 6-4, 4-6, 6-3 win, Goffin couldn't lay a glove on Federer as the clockwork Swiss purred through.

But both are safely into the quarter-finals, with Djokovic facing Kei Nishikori in his 27th consecutive Grand Slam last-eight clash and Federer up against Tomas Berdych.

Berdych also had to come through a marathon five-setter as he outlasted Spain's Roberto Bautista Agut 4-6, 6-4, 6-3, 1-6, 6-3 to reach the last eight for the sixth year in a row.

By comparison, Nishikori's win was a stroll as he crushed Jo-Wilfried Tsonga in straight sets, and he may fancy his chances against Djokovic after the Serb's flustered performance against Simon.

"It gives me great joy to know that I can't get worse than that, than what I played today," Djokovic said.

"I was obviously pleased to win the match, but in terms of the performance itself, I haven't done well at all... It's a match to forget for me."

He was at a loss to explain his tactic of continually trying drop shots, which either found the net or were returned with interest by the fast-moving Simon.

"Sometimes you have a brain freeze, if I can call it that way," the 10-time Grand Slam champion said.

Federer was in no mood to hang around in the evening's final match, watched by Australian great Rod Laver in the arena that bears his name.

"It was a good challenge and I'm happy I came out and played as well as I did... it was a good surprise out here tonight for me," Federer said.

Meanwhile, in the women's round, Serena Williams served up a glamour Australian Open quarter-final against arch-rival Maria Sharapova on Sunday as she looks to extend her iron grip over the Russian star.

The world number one and defending champion smacked Margarita Gasparyan 6-2, 6-1 in just 55 minutes on Rod Laver Arena to ensure the mouth-watering showdown.

Sharapova holds the dismal record of never beating her nemesis in 17 contests dating back 12 years. The last time she managed a win was at the WTA Tour Championships in 2004.

She now has another chance to finally get the monkey off her back after coming through a 7-5, 7-5 thriller against fast-rising Swiss teen Belinda Bencic.

The Russian world number five, who lost to Williams in the Melbourne Park final last year, said she was always looking to improve and used the losses against the mighty American to examine what she could do better.

"Absolutely. It's not like I think about what I can do worse!" she said.

"You're always trying to -- always trying to improve. I got myself into the quarter-final of a Grand Slam.

"There's no reason I shouldn't be looking to improve and getting my game in a better position than any previous round. It's only going to be tougher, especially against Serena."

A nonchalant Williams, who rarely looks beyond her next opponent in the draw, claimed she didn't know Sharapova was now in the way of her bid to win a 22nd Grand Slam and equally Steffi Graf's Open-era record.

"I'll be ready, she had a really good match -- I had no idea I was playing her [Sharapova] next," she told the courtside interviewer after taming Gasparyan.

"That will be a good match, I have nothing to lose. We are both doing the best we can. It'll be fun."