Mumbai City are now five points clear at the top of the standings over the second-placed Mariners right at the halfway stage of the league.
Bartholomew Ogbeche scored a 69th-minute stunner which was enough for the Islanders to get past their rivals and extended their unbeaten run to nine games. His goal was the first time that ATKMB conceded from open play this season.
Sergio Lobera made two changes to Mumbai's eleven with Cy Goddard coming in for the suspended Ahmed Jahouh while Ogbeche was a surprise inclusion ahead of Adam Le Fondre.
ATKMB coach Antonio Habas rang in three changes with Manvir Singh starting upfront. Glan Martins paired Javier Hernandez in the midfield with the latter making a comeback after last featuring against Odisha on December 3.
Mumbai City were dominant in the first session in terms of possession but despite some nervy moments in the game, ATKMB were lucky to walk into the breather on level terms.
The opening half was all about Mumbai's attack versus ATKMB's defence. But despite failing to register a single shot on target, the Mariners defended resolutely to keep the scoreline goalless.
Lobera's side forced an early scare on ATKMB's defence with their usual pace and high pressing game, creating an opportunity in the eighth minute.
Hernan Santana initiated the move and found Mandar Rao Dessai. The full-back kept his composure and squared the ball to Hugo Boumous, but the Frenchman's shot was straight at keeper Arindam Bhattacharja.
Mumbai City were inches away from taking the lead when Ogbeche diverted the ball from a goalmouth scramble. Luckily, Arindam was at the right place at the right moment to prevent the ball from entering the net with a goal-line save, leaving Lobera in disbelief.
ATKMB came back strongly in the second half and created a couple of chances. Edu Garcia had a big part to play. First he crashed his free kick from outside the box on target but Mumbai custodian Amrinder Singh dived full stretch to keep it out of the goal.
Garcia then saw his effort from open play hit the woodwork when he was set through by substitute Pranoy Halder, who replaced Martins at the break.
Mumbai finally managed to get past Arindam in the 69th minute and it was Ogbeche who produced a brilliant finish to give his side a deserved lead after being assisted by Boumous.
The Frenchman traded a one-two with Santana and played a back-heel pass to Ogbeche, who made his run and curled his effort into the top-right corner.
Mumbai's Mourtada Fall stood tall late in the game with vital blocks to deny Sandesh Jhingan and David Williams from finding the equaliser for ATKMB.
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