By Nick Mulvenney

MELBOURNE (Reuters) - Roger Federer made hard work of reaching his 27th consecutive grand slam quarter-final at the Australian Open on Sunday but it looked like a short shift after Francesca Schiavone's titanic tussle with Svetlana Kuznetsova.

French Open champion Schiavone took a gruelling four hours and 44 minutes to edge her Russian friend 6-4 1-6 16-14 in a Hisense Arena thriller and claim a place in the last eight after the longest women's grand slam singles match in the modern era.

Maria Sharapova would happily have played on longer in her fourth round match against Andrea Petkovic but the in-form German sent the former champion and world number one tumbling out of Melbourne Park 6-2 6-3 in just 79 minutes.

Defending champion Federer took his career record to 10-0 over Spain's Tommy Robredo but his 6-3 3-6 6-3 6-2 victory was not without its problems.

In hot sun on Rod Laver Arena, the 16-times grand slam champion raced through the first set in 32 minutes without losing a point on his serve.

Errors started creeping into the 29-year-old's game in the second -- his forehand particularly wayward -- and he conceded an unlikely break to allow Robredo to level the contest.

"I'm happy I'm still alive and going strong in the tournament, said Federer, whose run of successive quarter-finals now betters American Jimmy Connors' previous mark.

"It's a tough match. I knew Robredo was going to come out and hit a lot of loopy shots and make me earn it. He wasn't going to just give it to me ... I was able to battle through," added Federer who will play close friend and fellow Swiss Stanislas Wawrinka in the last eight after he battered American eighth seed Andy Roddick.

A record five Spaniards had reached the men's fourth round but at Melbourne Park but of the three who played on Sunday, only unseeded Robredo won a set.

Novak Djokovic was in dominant form as he steamed past 14th seed Nicolas Almagro 6-3 6-4 6-0 to set up a last eight encounter with Thomas Berdych, who thrashed a third Spaniard, Fernando Verdasco, 6-4 6-2 6-3.

Razor sharp Djokovic, the 2008 champion, dominated from the baseline, facing just one break point in the opening two sets then racing through the third in 28 minutes.

"It was a very good match," said the third seed. "Serve was great today, and it's important to raise a level of performance as I did today before the quarter-finals.

"Now the opponents are very difficult and matches are tough and unpredictable."

Sixth seed Berdych, another of a cluster of players snapping at the heels of the dominant Rafa Nadal and Federer, was also in impressive form in disposing of Verdasco and was talking up his chances of emulating his run to last year's Wimbledon final.

"Now I'm into the quarter-finals and I'm the one hunting the top players," Berdych, who beat Djokovic in the Wimbledon semis last year, told Reuters.

Kuznetsova had promised that she and Schiavone would fight like animals in their fourth round clash and she was true to her word as they clawed at each other for 284 absorbing minutes.

The 30-year-old Schiavone, the second oldest player to win a maiden grand slam, saved six match points in a three-hour final set before calmly pushing a forehand volley to settle the match.

"I hope one day to show this DVD to my son," said Schiavone, who will have a day to recover before meeting world number one Caroline Wozniacki in the quarter-finals.

"We work every day to do this -- to give the best when you really say, 'no, I can't do it'.

Sharapova has reached just one grand slam quarter-final since she won the last of her three majors here in 2008 and her game once again was lacking as she racked up 30 unforced errors against the dangerous Petkovic who celebrated a first run to the last eight with a cheeky dance.

"You know, not many things were working," said Sharapova. "I think it was just one of those days."

Wozniacki made a slow start against Latvian prospect Anastasija Sevastova but took command to win 6-3 6-4 before engaging in more jousting with the media.

The 20-year-old later made up an elaborate story about being scratched by a kangaroo before later apologizing to the media and admitting it had been a joke.

Petkovic will meet Li Na in the last eight after the Chinese, a semi-finalist here last year, continued her great run of form in 2011 by beating Victoria Azarenka 6-3 6-3.

(Editing by Martyn Herman and John O'Brien)