ATK got the better of Chennaiyin FC 1-0 in an ISL match at the Marina Arena in Chennai on Wednesday to go top of the points table.
ATK's David Williams scored the all-important goal in the 48th minute to seal the win on a day when Chennaiyin FC did everything but score, much to the dismay of their coach John Gregory.
Williams' strike was the ISL's 1000th goal.
The defeat meant that Chennaiyin are yet to find the back of the net so far in three matches this season.
ATK, on the other hand, moved to the top of the points table with six from three games, including a 5-0 demolition of Hyderabad FC.
Agustin Iniguez set up the goal for ATK with a diagonal ball down the right flank which was picked up by Prabir Das, who ran into the box and pushed it to Javier Hernandez.
Hernandez's shot was blocked by Lucian Goian. However, the ball flew to Williams who put the ball past the CFC custodian.
As expected, Chennaiyin mounted a fightback with coach Gregory throwing on Andre Schembri in place of Dragos. Around the hour mark, Edwin unleashed a powerful drive from a distance that had Arindam Bhattacharya scrambling.
A minute later, good interplay between Chhangte and Rafael saw the latter get to the byline and slide a ball across but nobody in a blue shirt could get a decisive touch.
Shortly afterwards, ATK were forced to tweak their game plan after Soosairaj went down with an injury and coach Antonio Habas responded by sending in Jayesh Rane.
Chances continued to come Chennaiyin's way but they let themselves down with their poor finishing. In the 72nd minute, a good bit of play between Thapa and Schembri saw the latter find space to shoot but he dragged his effort wide. A minute later, Rafael's cross was deflected goalward by Pritam Kotal but Arindam got down smartly to save.
Like in the match against Mumbai City FC on Sunday, Chennaiyin forwards missed numerous chances. Maltese forward Andre Schembri came close in the 72nd minute but failed to convert.
The hosts found a huge opportunity in the ninth minute itself. Nerijus Valskis had the goal all for himself after a cross but he missed.
After that, almost all the big chances fell to the visitors. ATK had a huge penalty shout denied by the referee when Roy Krishna was fouled in the box.
Though the teams started with intent, it was the home team that had the best of the chances in the opening period. Edwin Vanspaul found Nerijus Valskis with a cross in the third minute, only for the Lithuanian striker to head it over.
A deflection five minutes later sent Lallianzuala Chhangte in space down the left. His ball across the face of goal, however, could not be turned in by his team-mates.