Brazilian striker Cleo rounded the goalkeeper and stroked in an early opener and substitute Brana Ilic produced almost a blueprint copy in the 89th minute after a good solo run.
Serbia midfielder Radosav Petrovic, in the national team's provisional World Cup squad, put the icing on the cake with a header in added time with Partizan's fans already in raptures.
Red Star, who needed OFK to avoid defeat to keep alive any hopes of taking the title race to the final day, slumped to a 3-1 home defeat by top flight debutants BSK Borca.
The former European Cup winners took the lead through Brazilian midfielder Savio before the visitors, involved in a four-way battle to avoid relegation, struck through Vladimir Krstic, Aleksandar Djukic and Aleksandar Radunovic.
Mladi Radnik Pozarevac were relegated after a 4-1 home defeat by fellow strugglers Cukaricki Belgrade and Napredak Krusevac also boosted their chances of avoiding the drop with a 2-1 home victory over Rad Belgrade.
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