On the eve of the Australian Open, it was a 16th final for the Canadian and puts him one win from a sixth title.
Auger-Aliassime plays either second seed Sebastian Korda or Miomir Kecmanovic.
The loss kept American Paul from breaking into the top 10 for the first time in his career.
The semi-final was marred by more than 90 unforced errors, with Auger-Aliassime 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,” the winner 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.”
In the women’s draw, two-time Australian Open semi-finalist Madison Keys won 5-7, 7-5, 3-0 over Liudmila Samsonova to send her into a second final at Memorial Drive.
The 2022 Adelaide champion advanced when her heavily taped opponent retired in the third set.
“I’m excited to be in another final here,” Keys said. “I was really happy to stay in the match. She played unbelievable at the start.
“It’s not how you want to win (through retirement) but I’m glad I was able to stick around and tough it out.”
She faces either top seed Jessica Pegula or Kazakh Yulia Putintseva in the final.
© 2025 AFP