Struggling Reims stunned Marseille 3-1 on Saturday, opening the door to Paris Saint-Germain to win the Ligue 1 title later in the day.
Keito Nakamura gave Reims a surprise lead midway through the first half, before Mamadou Diakhon and Valentin Atangana added to the visitors' misery.
Valentin Rongier scored a spectacular goal to give Marseille hope in the final 15 minutes, but Roberto De Zerbi's side lost further ground on leaders PSG and are now 19 points behind in second.
The reigning champions are in action later on Saturday at lowly Saint-Etienne and, if they win, will wrap up the league title should fourth-placed Nice draw at third-placed Monaco in the day's final match.