The Cottagers saw off Norwich 3-0 in their third-round replay in London, and Hangeland believes it was a rare shut-out which was the most pleasing thing about a night which saw him making his long-awaited return from injury.
"For sure it's the clean sheet," Hangeland told BT Sport. "We've conceded far too many goals and one of our main targets was to keep that clean sheet today so we've very pleased.
"We need to find the right balance between attack and defence. Lately we've been conceding too many goals so hopefully this is step in the right direction."
Fulham held a 2-0 lead at half-time through goals from Darren Bent and Ashkan Dejagah before Steve Sidwell finished it off in the second half with his fifth goal of the season.
"We didn't feel comfortable at any time but obviously any time you score three goals you know you should win," Hangeland added. "Steve has had a terrific season so far with five or six goals from a central midfielder."
Hangeland had been missing for three months following back surgery, and admitted it had been frustrating watching Fulham's struggles from the sidelines.
"Funnily enough it's my first injury ever in 13 years of professional football, so yes, I'm happy to be back," he said.
Manager Rene Meulensteen echoed his captain's thoughts in praising Fulham's defensive efforts.
"The clean sheet, definitely," he said when asked for the main positive.
"We know it's an area we need to work address. We work ever so hard at it and made it one of our main targets today to make sure we were more solid, maybe a little less adventurous - to make sure we shut up shop, and apart from the first five minutes of the first half and the first five minutes of the second half I thought we did it pretty well.
"(Our desire) has never been in question but that desire and urgency has mainly been in going forward and it's cost us at times, particularly defending set-plays and counter-attacks.
"Today we made sure we were in good shape, working hard to get back into that shape and making it difficult...
"It's a good feeling after the unpleasant result against Sunderland."
Meulensteen was also asked about his January transfer plans, but would only confirm that a move for Ravel Morrison had been rejected by West Ham.
"We have put in a bid for Ravel Morrison but it was knocked back and we move on to other things," he said.