A change of guard did see ATK gain the upperhand as the defending champions, under interim coach Ashley Westwood, drew the first blood through new signing Martin Paterson in the 44th minute.
But after the changeover, Chennaiyin FC were quick to restore parity when Malison Alves' 51st minute header sneaked under goalkeeper Debjit Majumder before Jeje Lalpekhlua (64th) struck another for the visitors.
Coming off from a defeat at the hands of North East United FC, Chennaiyin FC dominated the show and returned to winning ways to pick their seventh win from 12 matches.
ATK, on the other hand, suffered their fifth defeat of the season to remain on eighth spot with 12 points from 11 outings.
More From This Section
In desperate measures, ATK had sacked coach Teddy Sheringham and named their technical director Westwood as the interim coach.
Under the former I-League winning Bengaluru FC coach, ATK made an anxious start as striker Ryan Taylor picked up a yellow card following a tough tackle on Raphael Augusto.
ATK enjoyed very little possession of the ball but still managed to take the lead just before half time through Paterson's header.
To make matters worse for ATK, Jeje put Chennaiyin ahead in the 64th minute, slotting home from close range after being left unguarded by ATK defenders.