Ferrer, the fourth seed in celebrated countryman Rafael Nadal´s absence, wore down Japan´s Kei Nishikori in straight sets to reach his third straight quarter-final at the year-opening Grand Slam.[break]
But 10th seed Almagro was only on court for over an hour before his Serbian opponent Janko Tipsarevic retired with a foot injury at 6-2, 5-1.
Ferrer, on track to face defending champion Novak Djokovic in the semi-finals, has never lost to Almagro in 12 meetings.
Djokovic was due to face Swiss 15th seed Stanislas Wawrinka in a night match later Sunday on Rod Laver Arena, with the winner to face Czech fifth seed Tomas Berdych in the semis.
Berdych defeated Kevin Anderson 6-3, 6-2, 7-6 (15/13) in 2hr 44min after surviving a nerve-racking tiebreaker in which the South African had five set points.
Ferrer, who will usurp Nadal as world number four after the Open, was far too consistent and disciplined for 16th seed Nishikori, winning 6-2, 6-1, 6-4 in 2hr 10min, but he dismissed suggestions he was in the top four on merit.
"I am top four because Rafael has been injured a long time. It´s true," Ferrer admitted.
"I think the top four, they are better. It´s my opinion. But I am trying to win every match. The results, are there, no? I´m not making something up.
"It´s very difficult for me to win a Grand Slam because there are the top four. At this time they are better than the other players."
Ferrer was promoted to fourth seed in the year´s opening Grand Slam when Nadal pulled out with a stomach virus, after missing all of last year after Wimbledon with a knee injury.
Although Nishikori had beaten Ferrer in their only previous Grand Slam encounter at the 2008 US Open, this time it was clear-cut for the Spaniard.
Nishikori´s exit ended Asia´s hopes in the men´s singles draw as he was bidding to repeat last year´s quarter-final appearance in Melbourne.
"He gets every ball, so I have to work 100 percent on every point and he also return well," Nishikori said of playing Ferrer. "It was hard to hold my serve. Yeah, it´s always tough to play against him."
Meanwhile, Almagro said he was disappointed to go through to his first Australian Open quarter-final at the ninth attempt because of Tipsarevic´s injury.
"I´m not completely happy because Janko was injured. That´s not the way you want to win," he said. "Sometimes you can´t do your best and you need to decide to stop if you want to be ready for the next tournament.
"I think he took the best decision if he´s really bad."
Radwanska storms into Open last eight
Fourth seed Agnieszka Radwanska powered into the Australian Open quarter-finals on Sunday with a straight-sets win over former world number one Ana Ivanovic.
The Pole won her 13th match in a row in beating the Serbian 13th seed 6-2, 6-4 and will face Chinese sixth seed Li Na for a place in the semi-finals.
The pair had played each other seven times before with Radwanska winning their four previous meetings, most recently in Beijing in 2011, and she once again proved far too powerful and consistent.
"I´m very happy I could play my best tennis today," she said.
"Ana played more aggressively in the second set and was volleying well but in the important moments I was focused and glad I could close it out in two sets."
Ivanovic, who won the French Open in 2008 and was a Melbourne finalist in the same year, has lost weight and boosted her strength during the off-season as she looks to rediscover her best form.
But she got off to a bad start against Radwanska, getting broken on her first service game in blustery conditions.
Some neat cross-court winners showed glimpses of the Ivanovic of old but the in-form Radwanksa was making few errors and giving her opponent even fewer chances as she worked her way to a 3-1 lead.
After the Pole went 4-2 in front on a dubious line call that Ivanovic didn´t challenge, she broke again in the next game and then took the set easily with an ace.
Radwanska, who is searching for her first Grand Slam title, maintained the pressure in the second set, breaking Ivanovic immediately, and there was no way back for the Serb.
She had chances to break in the fourth and sixth game but lacked the killer instinct in some entertaining rallies, with Radwanska wrapping up the match with an ace in 71 minutes.
Radwanska is the form women´s player this year after winning warm-up tournaments in Auckland and Sydney. Her best Grand Slam so far was Wimbledon last year when she made the final and was beaten by Serena Williams.
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