Novak Djokovic advanced to his sixth Australian Open final with a 6-1 6-2 3-6 6-3 victory over Roger Federer.
The world number one dominated the first two sets with some superb hitting, then had to hold off a spirited Federer fightback.
It is the third straight Grand Slam in which Djokovic has beaten the Swiss, prolonging Federer's wait for an 18th major title.
Djokovic will face Andy Murray or Canada's Milos Raonic in the final.
The Serb has beaten British number one Murray in the final on three previous occasions in the final, including last year's four-set victory.
"I played unbelievably in the first two sets but I needed to because Roger has been playing unbelievably and I knew he would be aggressive," Djokovic said.
Djokovic won 91% of points on his first serve in the first set, and 86% in the second
Before the match, much attention had focused on the first set, with Federer never having beaten Djokovic in a best-of-five match having dropped the opener.
But it was barely a contest as Djokovic twice broke the world number three in his opening three service games.
Pummelling Federer with deep groundstrokes and using clever changes of pace to induce 12 unforced errors from his opponent, the Serb wrapped up the set inside 23 minutes.
And he was no less dominant in the second, decisively breaking to love in the third game as he threatened to hand a rattled Federer one of his worst ever defeats.
Not since a 2001 loss to Andre Agassi at the US Open had Federer been limited to just three games in the first two sets.
Andy Murray's former coach Brad Gilbert praised Djokovic's performance in the first two sets as among the best of all time
This is the third Grand Slam in a row at which Federer has lost to Djokovic in four sets
But just when a Djokovic victory seemed inevitable, somehow Federer managed to reverse the momentum of the match to take the third set.
The 34-year-old held his opening three service games then seized his opportunity in a mammoth sixth game, missing three break points before finally breaking Djokovic at the fourth opportunity.
The fourth set was closely contested as a resurgent Federer threatened to extend Djokovic to five sets for the first time since their epic meeting in the 2014 Wimbledon final.
But a poor game at 3-4 ultimately proved costly as Djokovic broke and then served out to love to edge ahead 23-22 in his rivalry with Federer.
"My rhythm, my timing, all that, was a bit off in the beginning," said Federer. "He took advantage of that and did an unbelievable job for a long, long time tonight."
BBC tennis correspondent Russell Fuller
On the evidence of the first six rounds in Australia, not a lot has changed in the world of tennis since the end of last season. Serena Williams and Novak Djokovic still look a cut above the rest, although Roger Federer's rousing comeback thrilled everyone watching.
Djokovic made only six unforced errors in the first two sets - he was simply devastating. The rousing ovation Federer received as he came out to begin the third set sparked him into life, but the match was settled in the eighth game of the fourth.
Federer won the point of the tournament - playing a glorious half-volley, chasing down a lob, running down a smash, and hitting the line with a backhand pass - only for Djokovic to break and then serve his way into a sixth Melbourne final. He's won the first five, and will take some stopping now.