Castelen has been one of the Wanderers' most dangerous players this season and he has played a major part in the team's surge to the top of the table with six rounds to go.
Castelen, who is in his first season in Australia, has drawn criticism for his failure to find the net more often.
Before scoring the goal that broke the deadlock against Perth, the Dutchman had scored only once this season ... in Round 10 against Melbourne Victory.
"When you do not score it is hard but my game is different to that of an out-and-out striker," Castelen said.
"A real No 9 is there to score goals but I bring other things. I hold the ball up, I dribble, I create scoring chances and I make space for my teammates.
"When I'm not scoring it's not the end of the world because it is not the biggest part of my game.
"If I score it is always great, of course, because I'm betting into those positions so that is an extra part of my game that I can work on.
"It is always nice to score a goal but in every game I work hard and create a lot of chances.
"Every game I go out there and do the same thing ... I try and I try again."
"Today's was a great finish but above all it was a great effort from the team and a good win."
Castelen said he did not feel that the pressure to score more goals was getting to him because he actually took it as a positive that so many people expect him to crown his exciting attacking play with more goals.
"I think the fans and the media do appreciate what I bring to the Wanderers," he said.
"The fans keep wishing me to finish off the great chances that I get and I do not look at it negatively.
"Fans want me to score, perhaps 10 goals in a season, and we win the A-League and I'll be up there with the best players in the competition.
"I see this expectation as a compliment actually."
Castelen paid tribute to midfielder Mitch Nichols for the weight of the pass that enabled him to open the scoring after 62 minutes with a right-foot shot that went in off the far post.
"It was a very quick counter-attack and Mitch played a great ball to me," he explained.
"The speed of Mitch's pass was the key because if he played a slow ball the defender would have anticipated the pass and held up the play.
"My first touch was good and I had it in my mind what I wanted to do and I was confident when I hit the ball.
"I needed a bit of luck because the ball hit the post before it went in."
Castelen, who also hit the intersection of the post and the bar with a venomous shot towards the end, is fully aware that his contribution towards the Wanderers' win will not guarantee him a start in the next game against Brisbane Roar at Suncorp on Friday night.
Castelen replaced Dario Vidosic when the midfielder went off with a hamstring injury after 10 minutes and since the Socceroos player is unlikely to be fit for the Suncorp clash Castelen will be strongly favoured to regain his starting spot.
"It is up to the coach if I start or not," he said when asked if he had earned a start by his performance against Perth.
"Every week I play my game. I'm fit and it is important that when I'm asked to play I can play my game.
"I don't know why I did not start. Perhaps you should ask that question to the coach. His job is to pick the team and the rest is up to us.
"I don't go to the coach and ask him why I'm not playing. I just have to be ready for when I'm needed."