Making his debut for the Green and Maroons, Christopher Chizoba gave them an astounding 2-0 lead at half time with his twin blitz in the 20th and 45+1st minutes.
Post breather, Ram Malik (51st) extended the lead while their ace marksman Odafa Okolie (73rd) retuned to form completing the rout to hand Mohun Bagan their first win in six matches.
The biggest positive for Mohun Bagan was Odafa who set up three goals before finally putting his name to the tally.
There was more setback for the purple brigade as goalkeeper Ishan Debnath had to be rushed to hospital after colliding with their defender Deepak Mondal at the regulation time.
Virtually out of the title race, Mohun Bagan last won against Mumbai FC 0-1 in an away fixture on October 26 as the result, their third win from 12 matches, would take them to the top-half of the 13-team table.
Mohun Bagan now have 14 points, three less than United's tally after 12 rounds.
Not new to the Maidan having played with Kalighat and Peerless SC in the local league, Chizoba gelled well with Odafa upfront.
Goalless from three matches, Odafa too put up a positive intent right from the start as the duo combined well up front.
In a 20th minute move, Odafa surged past Mondal before squaring it to Chizoba who was lurking outside the box and had enough time to pull the trigger with a fine grounded effort.
Odafa was instrumental again when he set it up again for Chizoba who beat United SC goalkeeper before sliding it into an empty net.
The Mohun Bagan captain later seized the ball in the midfield before passing it on to Katsumi Yuta whose measured pass earned Malik a goal and a 3-0 lead just after the break.
There was no looking back for Mohun Bagan who toyed with the United SC defence at ease and Odafa completed the tally with a header.


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