Valentin Vacherot became Monaco's first ATP Tour singles champion and the lowest-ranked player to win a Masters 1000 event.
He beat his cousin Arthur Rinderknech in Shanghai, coming from a set down to win 4-6 6-3 6-3.
Vacherot, ranked 204, previously beat four-time Shanghai champion Novak Djokovic in the semi-finals.
He broke his opponent in consecutive games to lead by a break in the third set.
Rinderknech struck 12 winners and committed just two unforced errors in the opening set.
Author's summary: Vacherot wins Shanghai Masters.