Magda Linette will meet fifth seed Aryna Sabalenka in the Australian Open semi-finals after she beat Karolina Pliskova to continue her dream run.
The Polish world number 45 had previously never gone beyond the third round of a Grand Slam in 29 attempts.
But she produced a fearless display in a 6-3 7-5 win over Czech two-time major finalist Pliskova on Rod Laver Arena.
Belarusian Sabalenka defeated Croatia's Donna Vekic 6-3 6-2 to reach her fourth Grand Slam semi-final.
"I'm so emotional. I can't really believe it. It is really a dream come true. I'm super grateful and happy," Linette, 30, said.
"I will never forget this. This will stay with me for life."
Two-time Australian Open winner Victoria Azarenka plays Wimbledon champion Elena Rybakina in the other semi-final on Thursday.
Linette's dream Melbourne run continues
Many would have predicted Poland to be represented in the latter stages of the women's draw, given the form of world number one Iga Swiatek.
But while Swiatek's bid ended in the fourth round, Linette's best Grand Slam run extended to a fifth win at Melbourne Park as she dispatched former world number one Pliskova.
Well supported on the main show-court, the unflinching Linette recovered from being broken in the first game of the match to take control of the set, winning five of the following six games.
Her lack of experience in the second week at a Slam did not show as she saved a break point before serving out the set, with Pliskova tossing aside her racquet in frustration after dropping her first set of the tournament.
Having beaten world number four Caroline Garcia on her march to the last eight, Linette's confidence was evident against a misfiring Pliskova.
After saving two break points at 2-1 down in the second set, the Pole created three opportunities of her own in both the fifth and seventh games as she sought a decisive blow.
With Pliskova increasingly troubled by a wrist injury, Linette was eventually able to capitalise on a break opportunity before serving out the biggest win of her career.
"I think all my life I've been taking mistakes and losses very personally," Linette said. "My coaches did a really great job and I'm thankful to them because they put up with a lot."
Sabalenka overcomes tricky Vekic test
Although Sabalenka and Vekic arrived at their first Australian Open quarter-finals unbeaten in 2023, both players struggled for rhythm in a low quality first set littered with double faults and unforced errors.
Vekic admitted prior to the match that she had twice considered retiring from tennis after struggling to regain her form following knee surgery in 2021.
Her second major quarter-final, and first since the 2019 US Open, marked a significant milestone in her recovery.
However it was the big-hitting Sabalenka who was able to claim the key points to edge a challenging hour-long opener, with world number 64 Vekic taking just one of her 10 break point opportunities.
Sabalenka further tightened her grip on the contest with a double break to start the second set before Vekic hit back with a break of her own.
But Sabalenka quickly extinguished the Croat's faint hopes of a fightback, restoring her double break with a terrific forehand winner for 4-1 before eventually overcoming three break points to serve out the match.
"It feels really special to be in the semi-finals," said Sabalenka. "I'm super happy with the win."