Cousins Valentin Vacherot and Arthur Rinderknech will meet in the Shanghai Masters final after pulling off stunning upsets of former champions Novak Djokovic and Daniil Medvedev in the semi-finals on Saturday.
World number 204 Vacherot became the lowest-ranked player to reach an ATP Masters 1000 final after he defeated a struggling Djokovic 6-3 6-4.
Hours later, Rinderknech knocked out former US Open champion Medvedev 4-6 6-2 6-4 to complete an 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 cousin in Sunday's final.
"It was a dream that came out of nowhere,” Reuters quoted him as saying
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, who became the first player from Monaco to reach an ATP tour final in the open era.
Djokovic broke Vacherot in the first game of the match, but the 26-year-old immediately broke back and built a 4-3 lead, when the Serbian took his first medical timeout.
Vacherot won the next two games with ease to secure the first set, and put Djokovic through a 12-minute battle for the first game of the second set which the 38-year-old managed to win after saving two break points.
A double fault led to Djokovic losing his serve as Vacherot took a 5-4 lead that tipped the set in his favor.
"Such a pleasure to play at least once against you. Don't retire," Vacherot told Djokovic as both players shook hands at the net.
Four-times Shanghai Masters winner Djokovic congratulated Vacherot, 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," the world number five told reporters.
"So it's all about him. I wish him all the best in the finals and the better player won today."
World number 54 Rinderknech threw caution to the wind after losing the first set to former US Open champion Medvedev, getting an early break and saving five break points in a 12-minute game to go 3-0 up in the second.
Medvedev struggled with the 30-year-old Frenchman's strong returns, finding the net from the baseline multiple times as Rinderknech won the second set 6-2, with Vacherot watching from the stands.
A decisive break secured the third set for Rinderknech, as Medvedev saved the first match point with a 207km serve down the middle, but gave 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.
"I'm going to make him tired for tomorrow and at least I'm going to help (Valentin) to at least 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."
