World No.204 Vacherot set the ball rolling on the fairytale when he became the lowest-ranked player ever to reach an ATP Masters 1000 final by defeating a struggling Djokovic 6-3 6-4 on Saturday.
Hours later, Rinderknech, the world No.54, knocked out former US Open champion Medvedev 4-6 6-2 6-4 to complete the most extraordinary family double.
"I can't even say it's a dream because I don't think even one person in our family dreamt about it," Rinderknech said about facing his maternal cousin in Sunday's final.
"It was a dream that came out of nowhere."
Earlier, 26-year-old qualifier Vacherot troubled Djokovic with drop shots and punishing rallies and the Serbian fourth seed, struggling to turn, took medical timeouts during both sets.
"This is just crazy ... just to be on the other side of the court with Djokovic was an unbelievable experience," said Vacherot, the first player from Monaco to reach an ATP final in the open era.
"Such a pleasure to play at least once against you. Don't retire," Vacherot told Djokovic as they shook hands at the net.
Four-times Shanghai winner Djokovic congratulated his surprise conqueror, who is set to break into the top-50 in the world rankings.
"Going from qualifications, it's an amazing story. I told him at the net that he's had an amazing tournament, but more so his attitude is very good and his game was amazing as well," said the world No.5.
"So it's all about him ... The better player won today."
Rinderknech threw caution to the wind after losing the first set to Medvedev, getting an early break and saving five break points in a 12-minute game to go 3-0 up in the second.
Medvedev, who'd struggled physically over the week, found the 30-year-old Frenchman's returns a handful as Rinderknech took the second set with Vacherot watching on from the stands
A decisive break secured the deciding set for Rinderknech, as Medvedev saved the first match point with a 207km serve down the middle, but then tossed away the second with a double fault.
"I was like, you know what, maybe I'm going to lose, but I'm going to fight like crazy," Rinderknech said, after Vacherot had come down on court to enjoy an embrace with him.
"I thought I'm going to make him tired for tomorrow and at least I'm going to help Valentin try to start the match a little bit ahead physically.
"Then, somehow, I got the break and then another one finished the set and then I was like, you know what, I'm just going to try everything and give it my best and somehow it worked out."
