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.
Reims broke through in the 29th minute when Nakamura turned in the box and fired into the bottom corner for his ninth league goal this term.
Adrien Rabiot looked to have struck back for Marseille nine minutes later only for his goal bound header from a corner to be diverted to safety by the forehead of a retreating Sergio Akieme.
Despite their utter dominance as the match progressed, things went from bad to worse for Marseille as Reims broke on 51 minutes to double their lead.
Nakamura turned provider this time, galloping onto Junya Ito's pass and prodding the ball to Diakhon, who rounded the last covering defender before finishing emphatically.
The relegation battlers then had De Zerbi scratching his chin in disbelief on the sideline when they netted their third with just over 20 minutes remaining.
Reims struck again on the counter as Atangana raced onto Hafiz Ibrahim's throughball and slotted past Geronimo Rulli.
On 78 minutes, Rongier received the ball near the Reims box and surged forward, swerving between two challenges, before smashing the ball home.
However, the breakthrough came too late for the would-be title contenders as Reims held firm to see out a vital three points.
The upset leaves Reims still in 15th spot, but with a five-point buffer between themselves and the relegation play-off place.