ATK Mohun Bagan had to wait until the 90th minute to score past a stubborn Chennaiyin FC defence as the Mariners registered a hard-fought and crucial 1-0 win in the Indian Super League at the Fatorda Stadium, on Thursday.

Second-half substitute David Williams headed in a dramatic match-winner to help ATKMB move to 24 points, just two points behind leaders Mumbai City FC.

Both sides made a couple of changes coming into the game. Chennaiyin’s Deepak Tangri and Thoi Singh started in place of Anirudh Thapa and Edwin Vanspaul while Javier Hernandez and Manvir Singh were preferred over David Williams and Prabir Das by Habas.

The first half was evenly contested as both defences were at their best. Though there were few chances created, ATKMB was marginally the better team. Habas’ team sounded early warnings. After getting the ball in his own territory, Tiri ran forward and tried his luck from a distance, forcing Chennaiyin keeper Vishal Kaith to pull off a save.

Soon Chennaiyin had a chance. Esmael Goncalves dispossessed Carl McHugh and sent Rahim Ali through, but the youngster’s early shot went past the post.

Kaith continued with his rich form and was called into action late in the first quarter. Tiri played an aerial ball to the edge of the box. Edu Garcia headed it inside the box to Hernandez, who hit a first-time volley. But Kaith’s reflexes kept the ball from entering the net.

ATKMB enjoyed more possession, but play was mostly restricted to the midfield. Neither side was able to find the cutting edge in the box in the first session as they walked out goalless at the break.

While it was Sandesh Jhingan and Tiri for ATKMB, the defensive duo of Enes Sipovic and Tangri was brilliant for Chennaiyin at the back.

With 15 minutes left on the clock, Kaith produced a top-class save to deny Hernandez from taking the lead through a freekick. Lallianzuala Chhangte’s 85th-minute corner nearly put Chennaiyin ahead. But Arindam Bhattacharja made a crucial save before the Chennaiyin players could get to the ball.

The match looked to be heading to a draw, but with minutes left, ATKMB took the lead from a set-piece. Hernandez crossed in a perfect inswinging corner and Williams headed in to spark dramatic celebrations in the ATKMB camp.

Chennaiyin nearly scored the equaliser soon after when Eli Sabia dinked in a long ball inside the box for Sipovic, who managed to beat Arindam with his goal-bound header. However, Tiri acrobatically cleared the ball before it entered the goal.