Mumbai City scored once in each session through Matias Defederico (32nd minute) and Krisztian Vadocz (60th minute) to earn a comfortable win and a place in the play-offs with a match to spare for the first time.
Mumbai City FC are on top with 22 points from 13 matches and even if they lose their concluding clash against Delhi Dynamos on December 3, they are assured of a top four finish.
FC Goa (11 points from 11 matches), Chennaiyin FC (14 points from 12 matches) and FC Pune City (15 points from 12 matches) cannot overtake Mumbai's tally of 22 points even if they win all their remaining matches.
NorthEast United FC and Kerala Blasters play amongst each other later, which means atleast one of these two teams will fall behind Mumbai when they drop points.
Defending champions Chennaiyin FC were subdued and were never a good match. They lacked numbers whenever they attacked as Davide Succi was left isolated upfront.
Mumbai created several good chances and should have won by a much bigger margin. Sunil Chhetri, Defederico and Diego Forlan were all combining well and Chhetri went close in the 14th minute after trying to flick the ball past Chennaiyin FC goalkeeper Karanjit Singh.
The hosts moved up in the 32nd minute after Chhetri and Vadocz exchanged passes on the edge of the box, freeing up some space for the India captain to move into the box. His cross inside the goalmouth got a deflection and Defederico had no problem slamming the ball into the goal.
Mumbai's second goal in second session was a stunner from Vadocz. A cross from Diego Forlan saw Vadocz chest it down, escape the player marking him and smash a half-volley that beat the rival goalkeeper all ends up.
The scoreline could have been even bigger had Chhetri converted two chances from good positions. His first miss was in the 80th minute when Forlan did well to send an overhead ball which Chennaiyin defender Bernard Mendy missed but Chhetri was wayward with his attempt.
A minute later, Forlan fed Chhetri on the platter again but this time too Chhetri's attempt was way off target.
Defending champions Chennaiyin FC rarely troubled Mumbai goalkeeper Amrinder Singh, except for stray long rangers.