In Pool B, former champions Air India pulled off a narrow 3-2 win against local outfit Central Railway, while last year's runners-up South Central Railway, Secunderabad drew 4-4 with former champions Indian Oil, Mumbai.
The Army side showed promise at the start against ONGC and took an early lead when Robin H M flicked home the opening goal in the 14th minute.
Stung by that reverse, the oilmen from Delhi regrouped, got their act together and went on an all-out attack.
The Army side managed to close the gap when Bhushan Kujur scored a field goal in the 41st minute.
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But ONGC were not prepared to allow the armymen make a fight back as they pumped in three goals in the remaining period to close out the match.
Diwakar Ram (42nd) and Preetinder Singh (49th), both converted penalty corners, before Pramod Kumar hammered in the final goal of the match in the 68th minute.
For Central, both the goals came through full back Narad Bahadur, who converted the first penalty corner in the 34th minute and the sixth in the 54th minute.
Sunil Yadav (6th), Hamza Mujtaba (33rd) Roshan Minz (53rd) and Deepak Thakur (60th) scored for reigning Mumbai league champions Indian Oil against South Central Railway.
For SCR, the goals came through a brace from Poonacha M G (9th and 14th), Sandeep Singh (63rd) and Mayank James (65th).