Nigerian hitman Kalu Uche (3rd minute) and John Johnson (13th) put Steve Coppell's side 2-0 up before Carlos Salom (17th) pulled one back for the defending champions.
ATK, however, held out to hand Chennaiyin FC their fourth defeat of the season and climbed to the fourth spot on the Hero Indian Super League (ISL) table.
Chennaiyin FC got off to the worst possible start as a defensive mix-up saw them concede as early as the third minute. Chennaiyin goalkeeper Karanjit Singh's goal-kick was headed back by Gerson Vieira. It fell to Uche who found himself clear of both the centre-backs and slotted a calm finish past the goalkeeper.
ATK assumed control of the match thereafter as Manuel Lanzarote started to show his quality on the ball. He threaded a delicious ball for Uche in the 11th minute but the Nigerian's shot was straight at the goalkeeper. Two minutes later, Johnson met his wonderful free-kick into the box and headed into the far corner to double ATK's lead.
The setback forced the reigning champions into action and they pulled a goal back within five minutes through Salom. Francisco Fernandes' accurate cross from the right wing was glanced into the net expertly by the Palestinian striker as coach John Gregory heaved a sigh of relief.
Chennaiyin FC pressed for an equaliser and created several chances in the first half but failed to convert them. In an attempt to attack, they were leaving spaces behind for the likes of Lanzarote to exploit. However, ATK also could not capitalise on the offerings.
ATK looked a bit more compact at the start of the second half and Chennaiyin had to wait until the 56th minute to fashion a proper opportunity when Salom managed to dart into the box, only to see his rasping shot from close-range go well wide of Arindam Bhattacharya's goal.
The story of spurned chances continued for Chennaiyin FC as Andrea Orlandi saw a brilliant ball across the box just miss the outstretched legs of Salom and Issac Vanmalsawma.
At the other end, Lanzarote continued to threaten the Chennaiyin defence with his set-piece deliveries. One such effort saw Everton Santos send a header just over the bar.
Second-half substitute Gregory Nelson could have rescued a point for the Marina Machans when Thoi Singh found him at the far post with a cross. But his header was parried away by an alert Bhattacharya.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
