The Nigerian, who switched from United SC, gave East Bengal a 13th minute lead from a controversial penalty before completing scoring another a grounded header in the 50th minute in front of about 70,000 crowd in the high profile Calcutta Football League Premier Division clash.
For a team that was mired in controversy following its top official Neetu Sarkar's arrest in a chitfund scam, East Bengal coach Armando Colaco said it was a big morale booster.
"There were a lot of criticism on and off the field but I had faith, I am happy. Great feeling as it came from a derby against Mohun Bagan. It's just the beginning," Colaco said.
Ranti had a brilliant chance to complete a hat-trick, but missed a sitter in front of an open goal in the 75th minute.
Mohun Bagan had a jittery start when referee Pranjal Banerjee awarded a penalty to East Bengal after Cavin Lobo jumped over Fatai Adisa before falling down. Ranti cooly converted the resultant spot kick.
Mohun Bagan were quick to bounce back with C S Sabeeth scoring the 21st minute equaliser after Jeje Lalpekhlua's clinical centre ballooned over an air-borne Abhijit Mondal.
Mohun Bagan showed the intent with Japanese recruit Katsumi Yusa's brilliance from the left flank, but poor finishing cost them badly as their arch rivals snatched the lead through Abranches' freekick just before the break.
Luck also deserted Mohun Bagan as East Bengal took the lead with the goal coming from a Fatai deflection in the wall.
There was no looking back for East Bengal as Ranti took full advantage of a defensive lapse to score the third goal from Joaquim Abranches' cross.
"We just surrendered after conceding the third goal. We had full control and created chances but I'm very disappointed to lose a derby like this," Mohun Bagan technical director Subhas Bhowmick said.

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