NorthEast United were comfortably perched at the top of the table with two successive victories but were denied a rare hat-trick of wins after marquee player Diego Forlan scored the only goal of the match in the 55th minute from a penalty.
Mumbai City now share the top spot with NorthEast United but have a match in hand.
With matches in quick sucession, NorthEast United coach Nelo Vingada needed to do some reshuffling with the starting eleven and he chose to start with marquee Didier Zokoro for the first time and also gave the nod to the likes of Seityasen Singh and Argentinean striker Nicolas Velez.
The teams were cagey at the start and took time to gauge each other's strengths but on the basis of the first 45 minutes it can be safely said that NorthEast enjoyed the upperhand, or at least had the better chances.
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NorthEast midfielder Koffi N'Dri (Romaric) was the first to have a clear look at the rival goal but his left-footed volley from just outside the box was well-judged by Mumbai goalkeeper Roberto Neto.
The Mumbai goalkeeper was again called into action as Romaric was provided with plenty of space to execute another volley which was saved.
NorthEast defender Zokoro needed to come up with an instinctive tackle to thwart Forlan in a dangerous position and Aibor Khongjee had goalkeeper Subrata Paul diving frenetically to stop his long-ranger from sailing into the net.
The best chance of the match fell for Katsumi Yusa when Velez slipped the ball through for the Japanese, who shot it above the target from around the penalty spot.
In the second session, Mumbai City won a penalty after midfielder Pronay Halder was brought down by Regan Singh inside the danger zone and the referee had no hesitation awarding a spot kick.
NorthEast threw everything at their rivals in an attempt to secure the equalizer. They had chances too but Mumbai survived to register their second successive victory.