Desperate for their first win, East Bengal looked hungry for goals with Mahmoud Al Amna (14) and Eduardo Ferreira (19) giving them a 2-0 cushion at half time.
There was no let-up in their attack after the break as Laldanmawia Ralte (53rd and 65) completed a brace before Katsumi Yusa (79) converted a penalty to complete the rout and jump to fourth in the standings with four points from three outings.
East Bengal however missed out on keeping a clean sheet with Shillong Lajong's 19 year-old captain Samuel Lalmuanpuia converting from a curling freekick that beat goalkeeper Mirshad K at the far post.
Desperate for their first win of the season, Jamil rung in as many as five changes to the side that lost to Bagan.
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Jamil handed Cavin Lobo a surprise start, while Arnab Mondal and Mirshad were back in the starting XI.
Surrounded by two defenders, Al Amna made full use of an aerial pass in the box as he deceived the Shillong Lajong duo to put the ball at the back of the net with a spectacular finish, in what came off a slight deflection from Rakesh Pradhan.
In a space of five minutes, Yusa's corner from the right found the head of a rising Eduardo, who put the ball past goalkeeper Phurba Lachenpa without much fuss.
East Bengal continued to show sense of urgency and began the second half with a flurry of attacks.
But Shillong defence avoided any further damage with Lachenpa lunging ahead to keep his goal safe.
But it did not take long for the home side to bring up their third goal.
It was Ralte who put in another one from a lovely through ball from Al Amna as he dodged a charging Lachenpa, missed the ball for a second but regained his composure to put East Bengal in a driver's seat.
Sloppy defending from Shillong Lajong cost them a fourth goal with Ralte bringing up his brace.
There was more in store after a soft penalty was awarded to the home team as Redeem Tlang fouled Danmawia Ralte.
Yusa shot straight to Phurba but there was no looking back for East Bengal as the ball rolled inside taking a deflection.
But Jamil's wards could not maintain a clean slate and let in their third goal from set-pieces from three outings.
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