On the penultimate match day of the season, Mason Greenwood's 19th league goal in the 85th minute put second-placed Marseille back in the lead at struggling Le Havre. Amine Gouiri scored twice and Marseille won away 3-1.
Lagging one point behind Marseille, Monaco sealed their 18th win - 2-0 over Lyon - with goals from Takumi Minamino and Denis Zakaria and were also guaranteed to finish among the top three teams.
The first three qualify for the group stage of the Champions League, and the fourth team grab a spot in the qualifying rounds.
Gouiri scored Marseille's opener after halftime and the match was stopped soon after because of crowd trouble. Pressing to remain in the top flight, Le Havre pushed hard for an equaliser and got it when Issa Soumaré beat goalkeeper Geronimo Rulli from Josue Casimir's assist.
Greenwood's superb curled strike from outside the box put the visitors back on track and Gouiri gave more lustre to the win in added time on the break.
"At the start of the season, we had trouble playing at the Velodrome...," Marseille coach Roberto De Zerbi said. "We talked about it. The aim was to stay together, united, without putting football first. We spent some time together. We worked a lot on uniting the team and that showed on the pitch."
After getting past Arsenal midweek to reach the Champions League final, PSG coach Luis Enrique rested seven players: Gianluigi Donnarumma, Achraf Hakimi, Marquinhos, Nuno Mendes, Willian Pacho, Fabian Ruiz and Vitinha.
Senny Mayulu, an 18-year-old midfielder, was given a start and did not disappoint to put PSG ahead before halftime with a powerful strike. Ramos made it 2-0 off a deflection, and added another goal from the spot.
Having won the league with six games to spare, PSG are aiming for their first ever treble. In addition to the Champions League final against Inter Milan on May 31, Enrique's team will have another shot at more silverware against Reims the week before in the French Cup final.
Behind Marseille and Monaco, three teams were level on points; Nice, Lille and Strasbourg, who all lost on Saturday. Seventh-placed Lyon can still aim for the fourth spot but will need to win against Angers hoping that the trio of teams all lose.
At the bottom of the standings, last-placed Montpellier were already demoted. There was still a glimmer of hope for Saint-Etienne, who won at Reims 2-0. They remained in the relegation zone but just one point behind 16th-placed Le Havre, who were in the relegation playoffs spot.
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