Tsitsipas - playing in his first Grand Slam semi-final - comfortably held his opening service game. Nadal echoed.
But then he pounced. He gained the first break of serve after 11 minutes to lead 2-1. Around 20 minutes later the second seed was a set up and improving.
At 2-2 in the second set, he unleashed one of the shots of the tournament. Running out of the court to his left, he hit the ball around the net post for a clean winner. Tsitsipas looked to the heavens in disbelief.
The spectacular blow helped Nadal to three break points. But Tsitsipas showed mettle of his own. He reeled off five points inlcuding a sumptuous backhand volley to nudge into a 3-2 lead.
However the 20-year-old cracked when serving to take a 5-4 lead. Nadal served out serenely to seize control of the semi-final after 75 minutes.
And that turned into dominance at the outset of the third set when the 17 time Grand Slam champion claimed his opponent's opening service game.
Despite a few defiant winners, the Greek's odyssey through journeymen and a legend named Federer was ended.
"It's been a great tournament," Nadal said. "I think I have played very well every day. After a lot of months without playing, it is probably this court and this crowd that gives me that unbelievable energy."
If he is successful on 27 January, the 32-year-old will become the first man to win all four Grand Slams tournaments twice since tennis was opened up to professional players in 1968.
Tsitsipas is a long way from such heights. Playing in his second Australian Open and seventh appearance at a Grand Slam, he was attempting to become the first Greek player to progress to final in a major.
"Stefanos has everything to become a multi-Grand Slam champion," Nadal said. "When at 20 he is in the semi-finals - that says a lot of good things about him - and winning the matches that he won already. I hope to face him in important rounds in the next couple of years."