She came from a difficult position to land the spoils and equal the 1930s Gold Cup hero Golden Miller's record of winning the same race five years in a row.
And she was completing a first-day treble for trainer Willie Mullins and jockey Ruby Walsh.
Almost knocked over at the top of the hill, Quevega still had plenty to do at the final flight.
French raider Sirene D'Ainay looked to have the race in the bag when she touched down in front after the last after leading some way out.
But Quevega finally got going and she flew up the hill passing many rivals to get her head in front in the last 100 yards to win by a length and a half, with Swincombe Flame two lengths away third.
Walsh said: "We were very, very lucky.
"I'm not sure if she stood on herself or clipped heels with something else, but she was on the floor at the top of the hill - she nodded and I nearly fell over her ears.
"When she stood back up then, the boys were gone, and I had to sit and suffer down the hill, but she has a tremendous little engine.
"She has a wonderful attitude and you'd have to say she's trained by a genius.
"In fairness to her, she jumped the last and, my God, did she battle.
"I would have won very easily but for what happened at the top of the hill - when your luck is in, your luck is in."