Dempo, who led 2-0 at half-time, scored through Tolgay Ozbey(11th, 37th, 51st) and Romeo Fernandes(83rd).
Sporting Clube de Goa, who gave good account of themselves in the second-half, reduced the margin in the 77th minute through substitute Beevan D'Mello.
Thus Dempo, who won both their matches, have consolidated their position for a place in the semi-finals. While Sporting Clube de Goa, who lost both their matches, are yet to open their account.
Tolgay, who troubled the rival defense with his quick running, then increased the lead in the 37th minute from a penalty kick after he missed a close chance earlier.
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The penalty was awarded after rival defender Kofi Dankwae brought down Francis Fernandes inside the box off a cross from the left by Lenny Rodrigues.
Four minutes latter, Tolgay had a good opportunity to score a hattrick but his short was blocked by Sporting's keeper Sandip Nandy to have Dempo leading 2-0 at half time.
Just when Sporting were intensifying the pressure they conceded a penalty when defender Joyner Lourenco brought down Tolgay and referee Fasil Salen awarded the penalty. Tolgay converted it to give Dempo their second win.
Romeo Fernandes than rounded off the tally in the 83rd minute off a pass from substiute Alwyn George.
Sporting scored a consolation goal in the 77th minute from a free kick taken by substiute Beevan D'Mello.