The 35-year-old Spanish great, seeded sixth, was too solid for the Italian seventh seed, winning 6-3, 6-2, 3-6, 6-3 in 2hr 55min, and will face either Daniil Medvedev or Stefanos Tsitsipas in Sunday's final.
Nadal is level on 20 majors with his golden era rivals Novak Djokovic, who was deported on the eve of the tournament, and Roger Federer, who is absent with injury.
It gives the Spaniard an opportunity to go clear at the top and add to his lone 2009 Melbourne Park crown in his sixth Australian Open final.
"For me at the end it's about more than all these statistics, it's about being in the final of the Australian Open one more time. That means a lot to me," Nadal said.
"To me it's more important to be in the final of the Australian Open and fight to win another Australian Open than the rest of the statistics for the history of the sport.
"I just feel happy to be part of this amazing era of tennis, sharing all these things with another two players.
"That's it. In some ways it doesn't matter if somebody achieve one more or one less.
"I feel very lucky that I won once in my career here in 2009, but I never thought about another chance in 2022."
It has been an extraordinary effort from Nadal at the year's opening major, having to modify his game to compensate for a degenerative bone disease in his left foot that ended his 2021 season last August.
- 'It means a lot' -
He then caught Covid in December which, he said, made him "very sick".
Yet Nadal brushed aside Berrettini's challenge with precision shot-making, while last year's Wimbledon finalist could not overcome his sluggish start.
The stark statistic confronting Berrettini was that Nadal had never lost in his 20 Grand Slam semi-finals after leading by two sets.
"It means a lot to me to be in the final again here," added Nadal, who is now unbeaten in 10 matches to start the 2022 season after winning a warm-up event in Melbourne.
Nadal honed in on Berrettini's vulnerable backhand which contributed to 20 of the Italian's 39 unforced errors.
Berrettini, the first Italian man to play in the Australian Open semi-finals, raised his level in the third set.
He brought up his first break points in six sets in his two encounters with Nadal and broke with a forehand winner to 5-3 and served out to reduce the deficit to one set.
But the key break came in the eighth game of the fourth set, Nadal bringing up two separate break points and getting the crucial break when Berrettini netted a forehand before serving out for the match.
"It's amazing, I'm super happy to be able to compete for the last three weeks at this level," Nadal said.
"It's surprising for me to be able to play at the level that I am playing, but just compete and play tennis at the high level again, facing the most important players of the world, for me, it's something unbelievable.
"One month and a half ago I didn't know if I will be able to be back to the tour. So here I am, and thanks life for it."
Highlights Rafael Nadal Australian Open