While Wozniacki, 27, enjoyed the more comfortable outing against the unseeded Elise Mertens on Rod Laver Arena -- triumphing 6-3 7-6 (7-2) -- Halep dug deep once again to dispatch a rejuvenated Angelique Kerber 6-3 4-6 9-7 in an almighty scrap sure to be listed among the best of 2018 once the long campaign concludes.
It sets up a tantalizing battle between the world's two highest-ranked players Saturday.
Croatia's Marin Cilic meanwhile progressed to the men's final, topping surprise package Kyle Edmund of Britain 6-2 7-6 (7-4) 6-2 and awaits the winner of Friday's second semifinal between behemoth Roger Federer and another upstart, Hyeon Chung.
Halep, 26, just might be the player of destiny in Melbourne, since it was the second time the world No. 1 saved match points during her stay. On Saturday, the Romanian incredibly fended off three in succession to finally overcome plucky American Lauren Davis 15-13 in the third.
On all five of the match points, Halep played superb, aggressive tennis.
But some would argue the tennis gods are also on Wozniacki's side, given the Dane withstood two match points in a second-round win over Jana Fett and recovered from a considerable 5-1 deficit in the third.
Based on their head-to-head record, Wozniacki holds the psychological advantage over Halep, winning three in a row.
Two crowd-pleasers, two big movers
Battling back from the brink of defeat isn't the lone similarity between them.
Both will be competing in a third grand slam final and first in Australia after receiving their share of criticism for holding down the top ranking without ever bagging a major. They are two of the top movers around and only separated by a year in age.
Call them crowd-pleasers, too.
Halep, in fact, was voted as the WTA's Fan Favorite last season, ending the reign of Polish magician Agnieszka Radwanska.
Saturday's champion is guaranteed of holding down No. 1 in the rankings Monday, but for Halep winning a first major is the bigger target. Wozniacki presumably feels the same way.
It would be "bigger than No. 1," said Halep, enjoying a perfect 11-0 in the new season. "It's also my dream to win a grand slam title. But it's always tough when you are close. I had this opportunity two times. The last one was very close.
"Maybe Saturday I will be better. You never know. But if I make it again, the final, looks like I have enough power to redo this result and if it's not gonna happen Saturday, I will stay strong and I will keep thinking and dreaming for others."
Wozniacki wasn't dwelling on Saturday's potential result, either.
"I think it's been a great two weeks so far," she said. "I'm really happy and proud of how I've managed to turn things around when things weren't going my way and keep it up whenever it was going my way.
"I'm just excited. It's another finals. It's another great two weeks. Regardless of what happens now, I've done my best. When you go out there on Saturday, you have everything to win."
Halep has a history of playing in dramatic encounters at majors. Last year, for example, she relinquished a set and a break lead against Jelena Ostapenko in the French Open final and fell to home hope Johanna Konta in the Wimbledon quarterfinals.
Then in New York, an unseeded Maria Sharapova topped Halep in a lengthy first-round slugfest.
It looked like she would be on the receiving end of another painful reverse when Kerber broke in a lung-busting 26-shot rally to get to 4-5 in the third and proceeded to save two match points serving in the next game.
The 21st seed -- who had won 14 matches in succession -- manufactured two match points of her own serving at 6-5, only to see Halep escape. By this time, every rally seemed like a mini-marathon.
All the matches for Kerber already in 2018 appeared to have caught up with the newly turned 30-year-old. She lacked the usual pace on her serve and groundstrokes and left balls short.
Halep, however, was executing almost perfectly. There was no sign of apprehension or nerves, unlike in years past on the big stage.
Kerber saved a third match point but not a fourth, seeing her backhand sail long.
Halep finished with 50 winners and unforced errors, to Kerber's 33 winners and unforced.
"I feel more experienced," said Halep. "Also stronger mentally. And the way I play, it's different. I feel I'm more aggressive. I did 50 winners. Eight aces, if you can imagine. It's different, and I hope to keep this also Saturday."
'It was a battle to the end'
As disappointed as Kerber is sure to be, she'll leave Melbourne in much better spirits than 12 months ago.
Kerber struggled to back up her phenomenal 2016 but this year the former No. 1 has already registered more top-10 wins than in all of 2017.
"Of course I had the two match points, but ... she played good, so I couldn't do anything," said Kerber.
"It was just a battle at the end. It's just one or two points which decides the match.
"I gave everything. This is what I will tell myself in the next few days. And looking back what I achieved in the last three weeks, it was not so bad. (If I was) looking back four, five weeks ago, and somebody told me that I will win so many matches in a row, winning a title, being in the semis here, yeah, and still having the opportunity to win this match, as well...
"I think I will just take the positive things from the last three, four weeks and I'm looking forward."
Wozniacki suffered one of her most difficult losses at the 2011 Australian Open, losing when holding match points against Li Na in her only other semifinal in Melbourne.
And when Wozniacki couldn't serve it out at 5-4 in the second set against Belgium's Mertens, she was sure to have some self-doubt especially when the recent Hobart champion earned two set points at 6-5.
But on both Wozniacki produced two good serves and she played a flawless tiebreak.
She or Halep will be a grand slam winner Saturday evening.