But despite their evident relief at securing an unlikely victory, both Hughes and Fulham boss Martin Jol insisted much improvement is necessary in order to sustain their early momentum.
Jol admitted: "We have to do better in future to get results. You have to play your football and get out from the back and we didn't do that - but I was very pleased to get the points."
Hughes' rock-solid central defensive partnership with captain Brede Hangeland was the main reason the visitors managed to soak up the waves of attacks by the home side.
Boss Paolo Di Canio started with five of his summer signings and each impressed, with midfielder Cabral twice drilling just wide from long range, and right-back Ondrej Celustka bringing a stunning save out of Maarten Stekelenburg in the first half.
Kasami, a junior Swiss international who spent much of last season on loan at Luzern and only started at the Stadium of Light because Bryan Ruiz was jet-lagged after international duty, stole the show with the simplest of headers.
Hughes told Fulham's official website: "It wasn't vintage from us and I wouldn't put it down as one of our best performances but in terms of being resolute and strong and showing lots of character it is up there.
"To come up here in the first game of the season and come away with the three points is a big achievement. It's a confidence-booster for us and we look forward to doing it again next week."
Di Canio cut an increasingly frustrated figure on the touchline as his side did everything but discover the crucial cutting edge.