Mohun Bagan interrupted East Bengal's Calcutta Premier Division triumph party with a 1-0 derby win to end the local league on a high in front of more than 50,000 people at the Yuba Bharati Krirangan on Saturday.
Japanese recruit Katsumi Yusa struck with a left-footer to the far post late in the 83rd minute to hand Mohun Bagan their first win against the bitter foes in two years.
Mohun Bagan, who last beat East Bengal on January 7, 2012, in a local league tie, finished with 25 points, three behind their arch-rivals.
Having taken an unassailable lead of 28 points after their 2-0 win over Kalighat MS in the last round, East Bengal had confirmed a record 35th CFL title with a match in hand.
It was Mohun Bagan who impressed in the grudge match with a standout performance by goalkeeper Shilton Paul.
With Edeh Chidi and Ryuji Sueoka lurking in front, Paul saved Mohun Bagan several. But the winners suffered a setback just after the first-half when ace striker Odafa Okolie pulled out after a hamstring pull. With the Federation Cup beginning in less than a week's time, Odafa's latest injury will prove to be a big blow to their camp.