Dipanda Dicka gave the hosts an early breakthrough in the 20th minute and followed it up with another goal in the 65th minute.
The victory takes Lajong to nine points from six matches while Chennai remain static at four points.
Buoyed by two wins on the trot at home against Minerva Punjab and Mumbai FC, Lajong started the proceedings on a dominant note looking to control the game from the outset.
The first real chance came Lajong’s way when Dipanda crossed one back to Redeem Tlang whose shot got blocked.
Dipanda then put the home team ahead with a header.
Chennai did look like making a comeback towards the end of the first half but solid defending kept them at bay as they went into half time trailing 0-1.
Dipanda took the game away from the visitors by scoring from close range in the second half.
Chennai’s efforts thereafter to stage a comeback bore no fruit as the hosts romped home to another victory.