After showing only promise in their last couple of games, ONGC caused the season's biggest upset, bringing champions Dempo down to earth with a 3-1 victory in a sixth round I-League match at the Ambedkar stadium, in Delhi, on Friday.
Sorabuddin Mollick (12th), Jatin Bisht (58th) and Eric Brown (90+4) scored for the winners while Peter Carvalho got Dempo's consolation goal.
ONGC showed intent from the beginning, proof of which was the early strike, which, at the same time, also highlighted Dempo goalkeeper Subhasish Roy Chowdhury's poor work under the bar.
Mollick put the well-organised hosts ahead when he scored off a rebound after Kailash Patil's attempt off Brown's pass found Chowdhury.
Dempo fluffed a few chances in the period post the early goal, and there were also a couple of opportunities for the home side.
Dempo's hopes of a fightback went up in smoke after Bisht fired in a rasping volley from just outside the box, his class act giving OGNC a 2-0 lead moments from the start of the second half.
After a none-too-impressive outing in midfield, Carvalho reduced the margin down and gave Dempo a glimmer of hope when he tapped in Clifford Miranda's free-kick.
ONGC sealed the match when Brown found the net seconds before the final whistle, giving his side its first win in the league.
The key to ONGC's success was the domination in midfield. Dempo preferred to play a free-flowing game but ONGC's tight marking meant none of the Dempo players got enough space in the middle.
Man-of-the-Match Robin Gurung also deserves special mention for without his strong presence in defence ONGC could have found it difficult.
Dempo's Japanese Ryuji Seoka showed spirit but not opportunism, and he also lacked a dangerous striking partner.