The 18-year-old Mboko dropped to the court after Rybakina's shot sailed long on match point as the crowd - lined with "Allez Vicky" - erupted.
Mboko saved a match point in the third set and broke Rybakina twice to force the tiebreaker.
The youngster credited the jam-packed stadium with pulling her through the tense two hour and 46-minute comeback.
More than an hour of that was logged in the third set, and Mboko's fellow Canadians ebbed and flowed with every point she won, with cheers of "Allez, Vicky!" ringing out as they waved cardboard cutouts of her.
"I had everyone supporting me and pushing me through," she said in her on-court interview. "Without you guys, I don't think I would've been able to pull this through."
Mboko, ranked No.85 in the world, is seeking her first WTA Tour title and trying to join Faye Urban (1969) and Bianca Andreescu (2019) as the only Canadians to win the home event in the open era.
On Thursday night she'll face Japanese star Naomi Osaka, who beat 16th-seeded Dane Clara Tauson 6-2 7-6 (9-7) in the second semi-final.
Born in Charlotte, North Carolina, to Congolese parents, Mboko grew up in Toronto.
She upset top-seeded Coco Gauff 6-1 6-4 on Saturday to reach the quarter-finals, then topped Jessica Bouzas Maneiro 6-4 6-2 on Monday.
From Kazakhstan, Rybakina won at Wimbledon in 2022. She has nine career WTA Tour victories, winning in May on clay at Strasbourg. Rybakina beat Mboko 6-3 7-5 last month in Washington.
Mboko overcame 11 double-faults and battled through a wrist injury after stumbling awkwardly to the ground in the second game of the third set.
She will move up to at least No.34 in the world after starting the year outside the top 300.
Osaka, the four-time grand slam champion who reached No.1 in the world, continued her best performance in a WTA 1000 tournament since reaching the Miami final in 2022.
She stepped for 15 months toward the end of that season and had daughter Shai in July 2023. She's seeking her eighth title and her first since the 2021 Australian Open.
