3-6, 6-4 defeat on Saturday to Caroline Wozniacki was a double blow for the Romanian, who will also lose her number one world status to the Danish player when the new rankings come out next week.
The Romanian's forehand is the most potent groundstroke between the pair with 81 winners, and Halep has hit 24 more winners in total than Wozniacki during this tournament, but 50 more unforced errors.
Wozniacki is in her 43rd Grand Slam tournament and with a win will regain top spot, six years after last holding the position - the longest gap between stints at the top since computerised rankings were introduced in 1975.
ESPN will have live coverage of the women's final at 3:30am ET. She also has failed to make the breakthrough in a Grand Slam final, and so the stake couldn't be higher.
In another show of Wozniacki's enormous scrambling from the base-line, the Dane chipped a backhand from a clattered Halep fore, with Halep netting the return.
WTA Addict: "In this match-up, Halep and match Wozniacki in every way". So, yeah, these are two very successful players - no matter what happens on Saturday.
She was on Twitter immediately after Wozniacki finished off her win over Simona Halep to congratulate her for her first Grand Slam title.
The road to the final hasn't been an easy one for Halep, who suffered a sprained ankle in her first-round match against Destanee Aiava.
Halep is the current No.1 but the world No.2 Wozniacki, who was last on top in 2012, can return to the summit with a win.
There was a U.S. Open final loss to Serena Williams in 2014, five years after a teenaged Wozniacki fell to Kim Clijsters there in her first grand slam final. Top seed Simona Halep will face second-seeded Carolinze Wozniacki.
"You never know with her because she has insane good shots sometimes and also the serve". Caroline Wozniacki has that title forever now and she truly deserves it - she'll have a sense of freedom now and definitely huge relief. I played many times, yeah, like you said. But the one that really stung came two years later.
She was virtually flawless until she served for the set at 5-3, when the nerves kicked in and Halep broke back. It reportedly sold out on the online store soon after.
She later admitted thinking "it looks like it may not be my day" but she didn't let on, showing an abundance of grit and desire in the penultimate point of the match. She has made the US Final twice - and lost twice. The man does not have a poker face, and his expressions nearly deserve their own ESPN3 channel. They will want the title equally, desperately.
On hard court in the last 12 months, Wozniacki has held serve 4.1% more (75.4% to Halep's 71.3%) but broken very marginally less (43.8% to 44.9%), so based on these numbers, Wozniacki should be a slight favourite to take the title. They are familiar with being so close to victory, but not close enough. But I feel good, I feel relaxed, I don't feel the pressure of the match.
Wozniacki was the more assured player in the early stages and she quickly raced into a commanding 3-0 lead in Melbourne.