Giorgi, belying her ranking of world number 100, had defeated US Open champion Sloane Stephens in the first round, ousted twice Wimbledon and former Sydney champion Petra Kvitova and raced past Agnieszka Radwanska 6-1 6-2 in the last eight.
Kerber, who began previous year at top of the rankings before finishing at No.22, won her seventh straight match of 2018 after winning four singles matches at the Hopman Cup last week.
"I felt great yesterday; I felt like I played my best tennis probably all year. I mean, I'd love to go one further and hold the trophy up here, but, you know, I love playing in Australia, I love playing at home, it's nice to be able to get a lot of matches here and be rewarded with the final".
She slammed her racquet into the ground before being told off by the umpire, and just minutes later Barty had claimed the second set and levelled the match.
She will face Ashleigh Barty, who beat Australian compatriot Daria Gavrilova 3-6, 6-4, 6-2 in the other semifinal.
It will be the 19th-ranked Barty's second career title and her win over the 25th-ranked Gavrilova came after a topsy-turvy match that included 11 breaks of serve.
Kerber started 2017 ranked world number one but by the end of the season had slumped to 21, and she headed into the Sydney event ranked 22.
Versace Family Slams Second Season of American Crime Story
As the season has not yet aired, we can't say just how closely the show will adhere to the events as described in the book. Catch the premiere of The Assassination of Gianni Versace: American Crime Story on January 17 at 10 p.m.
"It's nice to make a final at home, but I think in my eyes it's flawless preparation for next week", Barty said.
The Queenslander's summer began with a first-round defeat in Brisbane last week but she has bounced back well ahead of the Australian Open, where she opens against world No.69 Aryna Sabalenka.
"We have set up a flawless platform for me to work with this year to try and go deep in tournaments, whether it's in Australia or in Europe or in the States".
"She's (Giorgi) beaten a lot of good players this week and so I was just trying to get a lot of balls back".
"I'm very happy, first of all, because life on ATP Tour is not easy. Still, I'm just trying to focus on every match, trying to learn from every single match", Kerber said.
Italian fourth seed Fabio Fognini set up a semi-final against qualifier Daniil Medvedev following a 7-6 (7-4), 6-7 (7-4), 6-2 marathon against Frenchman Adrian Mannarino.
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