Dempo, who dominated the match, scored through Clifford Miranda (15th minute) and Romeo Fernandes (35th) to register the win in the Group A league match at Nehru Stadium in Fatorda.
Dempo, who is leading Group A with nine points from three matches, is the second team to qualify for the semifinals after Bengaluru FC who progressed from Group B.
Mumbai FC, who finished their league engagements with four points from four matches, are now out of the tournament.
Jewel Raja, who was the livewire in the midfield, initiated the move from the centre and relayed the ball to Holicharan Nazaray on the right who send a cross deep into the box for Clifford Miranda to head home into the net.
Mumbai FC, who were pushed to defend themselves, had a chance to equalise two minutes later but Sampath Kuttymani who was free inside the box shot out.
Narzary, who worked hard on the right flank, worked his way on the right and tried to cross into the box, the ball hit a rival defender and Lenny Rodrigues relayed the ball to Romeo Fernandes who shot home into the net to give Dempo the 2-0 lead at half time.
Mumbai FC improved their game by several notches after the break but could not penetrate the rival defence. They showed lot of urgency in the closing stages.
