Nadal was resolute against the man who eliminated him from the US Open in 2015, securing a 6-3 6-4 6-2 win in Rod Laver Arena.
While the scoreline might suggest otherwise, world No 2 Nadal was tested by the flamboyant Italian, needing two hours and 16 minutes to progress to the final eight.
Fognini even led 4-2 in the second set, but Nadal’s counter-punching saw him avoid a more trying encounter.
Having overturned the second-set deficit, 2009 champion Nadal hit his stride in the final frame to wrap up the victory and move one step closer to his goal of a 21st major trophy – which would see him pull clear of rival Roger Federer.
Nadal entered the year’s first Grand Slam with a back injury but said after beating Britain’s Cam Norrie in the third round that the pain had begun to lessen.
The quarter-finals will see the Spaniard take on either Stefanos Tsitsipas or Matteo Berrettini, who meet in the fourth round later on Monday.
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