Unseeded Fernandez, who turned 19 on Monday, won 7-6 (7-3), 4-6, 6-4 to edge a tense semi against the Belarusian.
Fernandez, ranked 73rd, had already beaten defending champion Naomi Osaka and fifth seed Elina Svitolina.
Raducanu awaits Fernandez after she beat Greek 17th seed Maria Sakkari later.
After Raducanu continued her own dream run in New York, the pair set up the eighth Grand Slam final in the Open Era between teenagers.
It is the first since the 1999 US Open when Serena Williams beat Martina Hingis.
Fernandez clinched her place in Saturday’s final after showing all of her nerve and skill once again to beat 23-year-old Sabalenka.
On a raucous Arthur Ashe Stadium, Fernandez fell to the baseline in shocked celebration before giving a heart sign with her fingers as she lapped up the acclaim of the pro-Canadian crowd.
“My mental toughness has come from years and years of hard work and blood. On-court and off-court sacrifices,” Fernandez said.
“I just really wanted to be in the final. I fought for every point.”
Fernandez showed great resilience having fallen a break down early in the first set and having seen Sabalenka instantly wipe out a break in the final set.
But the outcome was as much down to Sabalenka, who has never reached a Grand Slam final, being overwhelmed by the pressure of the situation.(BBC)