She was down a break in both sets, saved three breakpoints at 4-4 in the second, rallied from 3-5 in the tie-break and saved a set point to finally defeat the Brazilian, 6-2, 7-6, in well over two hours.
Her 2023 tie-break record is now 3-2.
In contrast, none of the competitors in the previous rounds could force the top seed to even the 90-minute mark.
She moved past Cristina Bucsa and Claire Liu, 6-4, 6-0, crushed Wang Xinyu, 6-0, 6-0, in 51 minutes, gained a first-set retirement from Lesia Tsurenko and won last year's final rematch against Coco Gauff, 6-4, 6-2.
While her title defence is ongoing, she has already defended her world No. 1 status, for the short term at least.
Less than three years ago, the current 22-year-old became the youngest Roland-Garros champion since 1992.
Now, she has become the fourth-youngest woman in the Open Era to reach three Roland-Garros finals.
The Pole has enjoyed two successful title defences this season, beating Jessica Pegula and Aryna Sabalenka in the Doha and Stuttgart finals, respectively.
However, she is looking for her first 2023 trophy above WTA 500 level, having come short to familiar nemeses Barbora Krejcikova in Dubai and Aryna Sabalenka in Madrid.
She is 13-4 in career finals but lost three of six since the start of October.
Notwithstanding that, her major championship round win-loss stands at 3-0, with all three wins coming in straight sets.
She moved past Sofia Kenin and Coco Gauff in Paris in 2020 and 2022, and edged Ons Jabeur, 6-2, 7-6, in New York for her latest major.
Karolina Muchova had never made the second week of Roland-Garros.
Now, she just defeated the most in-form player of the season to reach her first slam final. It was a three-hour feast during which she rallied from 2-5 in the third set and saved a match point to beat Aryna Sabalenka, 7-6, 6-7, 7-5, despite some late cramping.
Her victory over the world No. 2 and Australian Open champion improves her career record against top three players to 5-0, with two of those scalps coming in Paris (Maria Sakkari, 2022).
It is a surreal moment for a player who had to be rolled out of court on a wheelchair due to an ankle injury at this very tournament a year ago.
The 26-year-old, who dropped out of the top 230 in August due to a long abdominal injury break, is slated to return to the top 20 and have a new best ranking.
She has pulled off a 25-7 win-loss in this season, including beating some good players in Paris: Maria Sakkari, Irina-Camelia Begu and Anastasia Pavlyuchenkova.
She has never played a final above WTA 250 level in her career. In May of 2019, the Czech lost to Jil Teichmann in three sets in the Prague clay-court show-piece despite home support.
A few months later, she defeated Magda Linette on the hard courts of Seoul, 6-1, 6-1, for what remains her only professional title above 10K level.
The world No. 43 has become the fourth outside top 40 ranked WTA player to reach a final at Roland-Garros after Renata Tomanova, a Czech, in 1976 (lost) and Jelena Ostapenko in 2017 and Iga Swiatek in 2020 (both won).
Players representing the Czech Republic are 1-2 in finals here, with only Barbora Krejcikova prevailing in 2021.
Head-to-head: Karolina Muchova leads 1-0. She defeated 17-year-old qualifier Iga Swiatek in the first round of 2019 Prague, 4-6, 6-1, 6-4, in two and a half hours.
The Pole, who is the 2021 doubles runner-up, is about to play some sort of final in Paris for the fourth year in a row and should be much more comfortable in her skin.
