The German made her breakthrough in 2016, with wins at the Australian Open and Flushing Meadows, but struggled a year ago, falling to 22nd in the world.
Kerber, who knocked out Venus Williams in her opening match in Sydney, said she was not yet back to her best form of 2016 when she won the Australian and US Opens.
Kerber drops just two sets throughout her week in Sydney.
The German will meet Italian qualifier and world No 100 Camila Giorgi, who upset Poland's former world No 2 Agnieszka Radwanska 6-1, 6-2.
Kerber defeats Ashleigh Barty 6-4, 6-4 in the Sydney finals.
America 'an idea, not a race,' senator tells President Trump
James Hunder, the president of the Liberian Organization of the Piedmont, said he was surprised that Trump made the vulgar remark. In short, they say, those countries are sh**holes, and due to their sh**holity, we need to allow immigration from them.
Barty was gracious in defeat, adding: "It's wonderful to see Angie back playing at her best".
Elsewhere, Elise Mertens defended her Hobart International title after a 6-1 4-6 6-3 win over Mihaela Buzarnescu. I played some of my best tennis this week and it wasn't enough.
The second-seeded Mertens, who won her maiden singles title in Hobart previous year as a qualifier, became the first player to win the tournament twice. "I am really looking forward to the rest of the year", Kerber said in a court-side interview after claiming a first title since her U.S. Open triumph.
De Minaur, ranked 167 in the world and the youngest player to reach an ATP World Tour final since American Taylor Fritz at Memphis in 2016, showed impressive fighting spirit to recover from 4-0 down in the decider to level the third set at 5-5.