Mason Robertson (33', 73') scored both the goals for the visitors whereas Sony Norde (42') was on target for Bagan with a sublime free-kick.
Shankar Lal Chakraborty rang in five changes after the 2-1 defeat to NEROCA FC. Aser Dipanda, Sankar Roy, Darren Caldeira, Azharuddin Mallick and Gurjinder Kumar were axed from the starting line-up after a poor show in Imphal. Sony Norde made a comeback after injury and slotted in at the left flank whereas Henry Kisekka started up front as the lone striker.
For Real Kashmir Mason Robertson was reinstated in the starting line-up and Gnohere Krizo was left out of the matchday squad.
It was one-way traffic for the entire first-half as Mohun Bagan started to dominate proceedings right from the first whistle. Chakraborty said that his team would go for three points in the pre-match conference and his team showed that they meant business.
Norde was showing flashes of brilliance whenever he got on the ball. Loveday Okechukwu and Aaron Katebe were given the responsibility to mark the Haitian and the duo did a decent job in marking him.
It was against the run of play that Kashmir scored the opener in the 33rd minute when Mason Robertson beat Arijit Bagui in an aerial battle and headed home a cross floated in by Surchandra Singh.
Bagan started pressing with more urgency after conceding and kept knocking on Kashmir's door for the equaliser.
It was Norde who brought the Mariners back into the game with a sublime free-kick that flew into the top corner while Bilal Khan could only stand and watch.
The second half started on a more even keel as Real Kashmir started pouring men in the attacking third.
On the hour-mark, Mason delivered an inch-perfect cross for Bazie Armand but the defensive midfielder could not keep his header on target.
Bagan got a number of set-piece in dangerous positions on the pitch but could not make them count.
In the 73rd minute, Mason scored his second after he was played through by Abednedo Tetteh. It was one gem of a strike from the Scottish player who brushed aside Abhishek Ambekar and fired a shot at goal which beat Shilton under the sticks.
Real Kashmir climb to the second spot with 21 points from 11 matches while Mohun Bagan continue to remain at the sixth position with 15 points.