But Nadal was strongly tested by the sixth-seeded Frenchman who broke his serve three times - matching Nadal´s total for the tournament - and had a set point with the Spaniard serving at 4-5 in the second set.
But Nadal was up to the task, ripping several winners on the run that were never inside the court until they landed and skipped away untouched.
Simon had won their last meeting in Madrid in October.
Nadal´s victory set up an all-Spanish semifinal after 14th-seeded Fernando Verdasco - the lowest-ranked player to reach the quarterfinals - beat No 5 Jo-Wilfried Tsonga, last year´s runner-up, 7-6 (2), 3-6, 6-3, 6-2.
Earlier in the day, second-ranked Serena Williams beat Russia´s Svetlana Kuznetsova 5-7, 7-5, 6-1 in extreme heat that was moderated a little by the air conditioning and closing of the Rod Laver Arena roof to enter the semifinals.
Williams, seeking her fourth Australian title and 10th Grand Slam championship overall, next faces Olympic gold medalist Elena Dementieva, who had to play her entire match with the roof open. The fourth-seeded Dementieva ousted Carla Suarez Navarro 6-2, 6-2 to run her winning streak to 15 matches after she won two tuneup tournaments.
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