Bashundhara Kings paid heavy price for some terrible defending as they were thrashed 4-0 by ISL giants ATK Mohun Bagan in their second Group D fixture of the AFC Cup at the Salt Lake Stadium in Kolkata on Saturday.

The Bangladesh Premier League champions, who started their campaign with a 1-0 win over Maziya S&RC on Wednesday, started the match brightly and had enough chances to take control, instead a number of ridiculous defensive error culminated in their first defeat in Asia's second-tier club competition.

Liston Colaco, the star Indian forward of Mohun Bagan, scored a hattrick before David Williams put the final nail in the coffin of Kings in the rain-affected encounter.

Kings forward Miguel Figueira had the first chance in the opening minute when he dispossessed Sandesh Jhingan in front of the box, but his effort missed the target by a few yards. Then Robson Robinho's freekick hit the far post on 18 minutes, following a long interruption due to lightning storm while Rimon Hossain saw his acrobatic volley from outside the box parried to the post by Mohun Bagan goalkeeper Arsh Shaikh on 21 minutes.

The cracks at Kings' defence soon started to open up as Colaco broke the deadlock four minutes later following a massive howler from makeshift centre-back Bishwanath Ghosh.

Colaco doubled the lead nine minutes later beating Kings' high-line defence before completing his hattrick eight minutes after restart, this time profiting from a childish mistake from Khaled Shafiei.

Yeasin Arafat saw his attempt saved by Mohun Bagan goalkeeper early in the second half before the left-back failed to guide Robinho's freekick into the net. David Williams soon completed the rout with a fine finish, smashing home on a cross from the left in the 76th minute.

Kings will play their last match on Tuesday against Gokulam Kerala, who had beaten Mohun Bagan 4-2 in the group opener.