Brazilian striker Marcelinho Pereira scored a superb hat-trick with goals in the 38th, 48th and 56th minute while Richard Gadze scored the other two goals to help Delhi inch closer to a place in the semi-finals.
Delhi, which have now moved to the second spot with 20 points from 12 matches, however, are not yet guaranteed of a semi-final spot as yet as three other teams (Kerala Blasters, Atletico de Kolkata and NorthEast United) can all overtake their points tally if results go their way. Delhi requires two point from their last two matches to stand a chance of qualification to play-offs.
In the first half of the Sunday match at the Jawaharlal Nehru Stadium, the teams were tied 1-1 after Fulganco Cardozo gave Goa the lead in the 31st minute but Marcelinho equalised seven minutes later.
Delhi's domination in the second session, however, stunned FC Goa as they conceded four goals in nine minutes.
Goa surged ahead just after half an hour's play through Fulganco who tapped the ball inside an empty goal. Delhi equalised within seven minutes from a well-worked free-kick.
Florent Malouda chose to slide a ball through for Pereira on the left and the Brazilian striker made no mistake slamming the ball past Goa goalkeeper Laxmikant Kattimani.
In the second session, there was a complete transformation as Delhi scored four goals in nine minutes. Pereira started Delhi's goal run in the 48th minute.
He got a ball about 25 yards out, cut past Richarlyson who was marking him and then sent a rasping drive that beat Kattimani for the second time.
Gadze scored his first of the night in the 51st minute after Pereira turned provider and the Brazilian himself completed his hat-trick in the 56th minute.
Gadze made it 5-1 in the 57th minute, beating the challenge of Raju Gaekwad and scored his second goal of the night.
The defeat left FC Goa rooted to the bottom with 11 points from 13 matches and they will be hugely embarrassed after suffering their biggest defeat in ISL.