Ferrer, 30, slipped two-sets down against fellow countryman Nicolas Almagro on Rod Laver Arena centre court on Tuesday but recovered to take the match 6-2 in the fifth set in three hours and 45 minutes.
Ferrer came back strongly from his stuttering start to take the match 4-6, 4-6, 7-5, 7-6 (7-4), 6-2 as Almagro faltered in the final set with a groin injury.
Almagro was troubled from late into the fourth set with increasing groin soreness and could hardly run from side-to-side in the final lop-sided set.
He required court-side medical attention to his strain and limped noticably at times early into the fifth and deciding set.
Ferrer, the tournament number four seed, enters the last eight championship contenders and on track to a likely semi-final showdwon with reigning champion and tournament number one seed Novak Djokovic.
Djokovic confronts number five seed Tomas Berdych in their quarter-final for a place in the semi against Ferrer.
In the other side of the men's draw unseeded Frenchman Jeremy Chardy confronts number three seed and strong contender Andy Murray in one quarter-final with Jo-Wilfried Tsonga up against 18 times Grand Slam championship winner Roger Federer in the other final-eight shootout.