Second-half goals from Steven Fletcher, Carlos Cuellar and Stephane Sessegnon gave the Black Cats their first win since September and O'Neill wants the new-found momentum to roll into next weekend's game against high-flying West Brom.
"It's very pleasing to get the win away from home - I would have taken the win in any shape or form, but it was a good win today and we scored some good goals," he said.
"The players are looking forward to the next couple of games at home. It's always a good atmosphere at the Stadium of Light.
"Winning today is a boost of confidence ahead of a very important game next week."
The win moved Sunderland up to 15th in the table but prevented Fulham being able to move ahead of the likes of Tottenham and West Ham into seventh.
Cottagers boss Martin Jol felt his side were good enough to have taken the lead before Hangeland's red card for a reckless lunge on Lee Cattermole.
"Maybe we should have scored once or twice but it was difficult when we had someone sent off with 15 minutes to play in the first half," he said.
"It was very disappointing to concede the first goal because with ten men it is difficult to play in their half and to take the initiative.
"We had to make the decision whether to make the balance in the team again or to go for it with three centre forwards and I tried that and it paid off."
Jol, who saw substitute Mladen Petric level the scores at 1-1 for a brief period in the second half, also felt referee Lee Probert was not consistent in the game and reckons Hangeland was unfortunate to be dismissed.
He said: "There were more incidents. There were one or two players with four or five fouls before he booked them in the first half.
"By the letter of the law, two feet off the ground is a red card. But he slipped with his right foot, he was under the ball, not over it, and then his second leg came. I don't think it was a red card."
Hangeland now faces a three-match ban while Jol is also likely to be without Alex Kacaniklic and Bryan Ruiz for at least three weeks as both had to be substituted after suffering hamstring injuries during the game.