The fascinating confrontation between Adelaide's defence, the best in the A-League this season, and Melbourne City striker Fornaroli's brilliant goal-scoring ability will occur in the semi-final at Coopers Stadium on Friday night, with a place in the grand final up for grabs.
Fornaroli smashed the competition's regular season goal-scoring record with 23 in the 27 rounds and then added two in City's 2-0 win over Perth Glory in an elimination final. They were both superb efforts, from a bicycle kick and a free-kick.
But Adelaide had kept Fornaroli scoreless in the final round, beating City 2-0 to ultimately claim the Premiers' Plate once Brisbane Roar, the leaders going in, were only able to draw their game 0-0 against Melbourne Victory.
Asked if he was confident United could again stop Fornaroli from scoring, La Rocca replied: "Yeah, we're confident, but we know he's a quality player and one of the best in the A-League and it won't be easy, because if you just switch off for one second he can punish you.
"We have to stick together because we know if we work together we can do a good job. It's not easy, because when you're on the pitch you know this player or that player is trying to out-think you and a player like Fornaroli has got the ability to change the game at any time.
"You have to concentrate and think hard and I have to be confident Dylan (McGowan, Adelaide's other central defender) can cover me and he has to be confident I can cover him, but this is the strength we have.
"There will be times when I have to pick him (Fornaroli) up, and times when Dylan has to, and probably times when either fullback has to as well, because he's a player who moves around the box trying to get free.
"This is where the understanding we have between us as defenders is very important. We can't afford to get it wrong."
La Rocca, who before joining Adelaide this season had three years with Western Sydney Wanderers and was in the starting line-up when they won the final of the 2014 AFC Champions League, said he had been deeply impressed by McGowan.
"Dylan has had an unbelievable season," La Rocca said. "I didn't know him previously, but he has done very well. All the defenders here have done a good job. Everyone knows what they have to do and we support each other well."
Adelaide's back four and goalkeeper Eugene Galekovic will obviously depend on the entire Adelaide team working hard in defence, starting with Bruce Djite up front, to make it as hard as possible for City to build up and get the ball to Fornaroli in threatening positions.
The success of that will largely depend on Adelaide's ability to make it difficult for City to supply good ball out of the back to playmaker Aaron Mooy and, when Mooy does get the ball, limiting his time on it. United did that very well in the last-round game.
Finals football was obviously foreign to Italian-born La Rocca before he came to Australia to join Wanderers, but he said he loved the concept and thrived on the added pressure that playing in such must-win games brought.
"Everyone is watching you and I like that sort of responsibility," he said. "People say every game you should be like this, you should play every game like it's a final, and I do try to be that way, but when it's like this, when you have to win, I think you manage to give even more."