Felix Auger-Aliassime needed four match points and nearly three hours to beat Tommy Paul 7-6 (7/3), 3-6, 6-4 and reach the Adelaide International final on Friday.
On the eve of the Australian Open, it was a 16th final for the Canadian and puts him one win from a sixth title.
He will face second seed Sebastian Korda, who defeated Serb Miomir Kecmanovic 6-4, 7-6 (7/4).
Paul's loss prevented the American from breaking into the top 10 for the first time in his career.
The semifinal with Auger-Aliassime was marred by more than 90 unforced errors, with the Canadian failing to close out a straight-sets win when Paul won six of the last seven games in the second set.
"I'll try and recover now for the final," Auger-Aliassime said. "The match was about physical and mental effort. There were a lot of ups and downs.
"It was not the best level from either of us, but sometimes matches are like that, you have to find a way through."