Boithang Haokip made no mistake in converting a free kick from 40 yards with a curling shot in the 14th minute of the match.
A Lajong defensive lapse let Jackichand Singh nearly equalize from a Seitya Singh cross at the near post six minutes later.
From then on, the hosts were found wanting and their star goalkeeper Rehenesh Singh, who did well in the recently concluded Hero ISL campaign, was busy foiling several Wahingdoh raids.
Returning from the break, the lightning fast Jackichand's cross found Seityasen Singh within the box, who made no mistake in netting it from just under the top bar.
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Sensing trouble, Lajong's manager Thangboi Singto pumped in Cornell Glen and Assam's striker Durga Boro and their induction made an impact right away.
In the 64th minutes, Glen missed the net by a whisker when Boithang cut in with a beautiful cross. Five minutes later, Semilen Doungel missed two chances to create magic for his side.
Boithang's effort to equalize went off in vain again in the 78th minute when his free kick went a little wide.