The summer signing arrived at Shamrock Park with the weight of expectation on his shoulders as Ronnie McFall's first high-profile capture since the club's fall from senior level.
The former Linfield midfielder kicked off his IFA Championship debut by finding the net against Armagh City but has just two goals to his name entering tomorrow's (Saturday's) crucial trip to Coagh United.
A slow start to life with the Ports has resulted in some criticism from the sidelines and Mouncey accepts the validity of the supporters' views. But now he is planning to win any sceptics over by getting back to his best.
"Fans pay the money over the turnstiles so have every right to criticise," said Mouncey. "I am willing to take that on board and, if I am brutally honest, I have not been playing well.
"However, my season has only really started in recent games because when I joined Portadown it was off the back of a few months out with injury.
"I don't want to hide behind any excuses but my injury problems meant it was always going to take time to get back to form.
"I have to say, the IFA Championship is pretty intense and requires a period of adjustment.
"But I'm starting to feel good again and can go into games full of confidence. Now I want to show what I am really capable of on the pitch.
"I need to prove myself and the weekend match against Coagh is a perfect platform as it's our biggest game so far this season due to the league standings."
Mouncey feels Portadown are improving with each game and starting to adjust to the IFA Championship's unique challenges.
"Fans may expect us to win six or seven, but the IFA Championship presents its own difficulties and everyone has to settle," he said. "One of the things I picked up from my time at Linfield was the drive to win ugly.
"We went out to win rather than just play pretty football. The points were all that mattered.
"It's the same in any level; Arsenal play some of the best football around but that hasn't helped them win trophies in recent seasons.
"Hard work is the only way we can expect to get out of this division.
"The players really appreciate the support from the fans and it was great to hear so much singing and backing against Larne.
"They would probably be surprised at how much fans can influence events and spur the team on."
Kick-off tomorrow (Saturday) will be 2.30.