"Because we got challenged, one, by a very spirited team, and then we had our own internal challenges in terms of changes.
"We kept a team to 10 points in what were difficult conditions. In previous weeks we didn't have to deal with that, a lot of stuff went our way.
"Tonight was probably the first time we've really had to go right to the death in a while and we found a way to win and that's important."
The second-ranked Sharks will present a truer test of their finals credentials, with Cronulla unbeaten at home this season and enjoying a 10-game winning streak.
The Warriors will need to be at their disciplined best at Shark Park with Shane Flanagan's side revelling in closely fought contests while also possessing the strike-power and flair to punish sides from all areas of the field.
McFadden was unsure if Leuluai would be fit to play, while Queensland interchange prop Jacob Lillyman will need to back-up from Wednesday's second State of Origin encounter in Brisbane.
The Sharks will be sweating on their four New South Wales players remaining intact, with captain Paul Gallen, five-eighth James Maloney, centre Jack Bird, and damaging forward Andrew Fifita vital to maintaining their momentum.
Meanwhile, rookie Warriors front-rower Toafofoa Sipley has escaped suspension despite being cited for a chicken-wing tackle on Roosters forward Kane Evans.
The grade on dangerous contact charge attracts 75 penalty points with an early guilty plea, meaning Sipley will be available if required for the trip to Sydney.