The Dutchman, who headed home an equaliser three minutes from the end then set up his captain Richard Brittain for the winner deep in injury time, believes this could be the catalyst for him to stake his claim.
He said: "It was a nice last five minutes. It is lovely to do something for the group and to do it like this for the team - and for me also - was great.
"We can enjoy the win tonight, but then move on to next Saturday and another away game. We hope this is the boost we need.
"It's important to know as a team that you are never beaten. It is never over until the referee's whistle sounds. Before that, everything is possible."
De Leeuw admitted it is difficult being left on the bench.
He said: "It is hard to be a substitute all of the time and you just try to do the right things coming off the bench. But today is my lucky day, I showed what I came here for. If this is the catalyst for me to do well for the team, I'm happy.
"I hope this can be the breakthrough for me. I train hard every week. Everybody does.
"It was a must-win game today because the other clubs were on eight points and we were four. Now we are closer to them in the table. It also means we leave Hearts a good distance behind, which is good."
Hearts forward Callum Paterson said: "We're absolutely gutted. They had pressured us, but never really looked like scoring.
"It was just two silly mistakes right near the end of the game that has cost us dearly.
"It has cost us three points we desperately needed. I had a wee chance just before Jason Holt's chance. There were numerous occasions we could have scored and put the game to bed.
"We just didn't take our chances."
Paterson believes the young side can learn from this setback.
He said: "There is never a good time for something like this to happen, but we can take a lot from the performance.
"It has happened, and we need to learn from our mistakes and make sure it doesn't happen again throughout the season.
"We're learning all the time. Take Jamie Hamill and Jamie MacDonald out of the equation and we have probably played 50-odd first team games between us.
"We're learning in every game - and we just need to keep learning."