After winning her way into the main draw through qualifying, the Australian No.1 had been preparing for what shaped as a difficult first-round encounter with 13th seed Anna Kalinskaya.
But only minutes before taking to Kia Arena on Tuesday, Birrell learnt that the Russian had withdrawn due to illness, and she would instead be facing qualifying lucky loser Eva Lys from Germany.
It all quickly went south from there.
Kim Birrell admitted she did not handle a last-minute change of opponent at all well. (Joel Carrett/AAP PHOTOS)
Birrell only held serve once in eight attempts as she crashed out 6-2 6-2 to the free-swinging German, almost without firing a shot.
"Absolutely (it threw me)," said Birrell, who was unable to hold back the tears in her post-match press conference.
"I had prepared to play Anna, who's a really amazing player.
"I knew that I was in for a battle against her, and I had done my research and spoke a lot with my team but, unfortunately, that isn't who I faced today.
"Then to find out that she withdrew and that I was playing someone completely different, it did rattle me.
"But in saying that, she was in the same position as me - she didn't know who she was going to be playing, so we were both put in pretty tough situations.
"I take responsibility for not handling that, and credit to her."
Lys had only won one of her previous six grand slam matches.
But defying that poor record at the majors, the 23-year-old grabbed her unexpected opportunity with aplomb, quickly silencing the pro-Australian crowd.
Eva Lys celebrates her dominant win over Australian Kim Birrell. (Joel Carrett/AAP PHOTOS)
Swinging hard from both wings, the German completely dominated the winners count 20-4.
In contrast, an out-of-sorts Birrell was only able to hold her serve once in eight attempts in a match that flew by in just one hour and 10 minutes.
"It felt like it just got away from me," said 26-year-old Birrell.
"Beforehand, I think my nerves elevated quite a bit.
"Then when you've got the nerves going, your tendency is to do the opposite of what you need to, and you just rush.
"It is one of those tough situations and something that I can definitely learn from."
In eight previous appearances at the grand slams, Birrell had only recorded three victories - all of them at Melbourne Park.
Teenaged star Emerson Jones was also handed a brutal reality check on her grand slam debut, going down 6-1 6-1 to No.6 seed Elena Rybakina.
The 2022 Wimbledon champ showed no mercy to the 16-year-old Australian wildcard, closing out the match in 53 minutes.
Emerson Jones' major debut was a baptism of fire. (Lukas Coch/AAP PHOTOS)
Rybakina still found time to praise her young opponent.
"She is very young and I think she has a great future and many more years on tour, but I'm pretty happy with my performance," Rybakina said.
"I've watched her matches, of course. When you don't know the opponent, at least me, I'm trying to focus on myself, and I know that serve is a big key in my game.
"So I was focusing on that. I needed a couple of games to get used to her shots. She is very talented."
On the men's side, 2023 Australian Open doubles champion Rinky Hijikata spurned a golden chance at a second-round berth with a 6-4 6-4 6-3 loss to qualifier Mitchell Krueger, ranked 74 spots below him.
The 31-year-old American could face another local in the form of Alexei Popyrin in the second round, if the 25th-seeded Australian can overcome Frenchman Corentin Moutet in Tuesday evening's headline act on John Cain Arena.
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