He was broken when serving for the championship at 5-4 in the fifth set but made no mistake the next time.
At 5 hours and 24 minutes, it was the second longest Australian Open final after Novak Djokovic beat Nadal in five sets in 5 hours and 53 minutes in 2012.
The 35-year-old Spaniard now has one more than Roger Federer and Djokovic, his long-time rivals in the so-called Big Three.
With the 2-6, 6-7 (5), 6-4, 6-4, 7-5 win that started Sunday night, was delayed in the 84-minute second set when a protester jumped onto the court, and then finished early Monday morning, Nadal also became just the fourth man in history to win all four of the sport's major titles at least twice.
2005, 2006, 2007, 2008, 2010, 2011, 2012, 2013, 2014, 2017, 2018, 0219, 2020