"It is a big stepping-stone, especially as an amateur, to compare where we are against what we have got in New Zealand, with people who have been doing great things like Mark Brown and [Jennian Homes Charles Tour winner] Dan Pearce," he said.
"It just shows I can compete with them."
Mountcastle credits some local knowledge as a factor in his success.
"I know the course well as I come up here quite a bit and work with Jay Carter and George Wardell in the P1 Academy. It does help because you just know where to hit it and where the best spots are. It didn't always work out but it is always nice to know where to go."
Tauranga-based Brown was chasing his fourth straight win in the tournament and fifth overall but was unable to get anything going.
Despite shooting his second special round of 59 at the event on Friday he was unimpressed with his form overall.
"I just didn't play well all week really. Apart from a stretch of 10 holes on Friday it was pretty average. Kerry played well so congrats to him and great to see an amateur come through and win one of these," Brown said.
"I just didn't have enough good chances today and didn't make enough birdies. It was just one of those things."
In the women's division, Titirangi amateur Brittney Dryland, 23, led from start to finish to win her first title at Tauranga and her second on the Charles Tour.
Her four-round total of 10-under 278 easily won by five shots from Miree Jung, with Carmen Lim a shot further back.
"To be honest because I have had three tournaments in a row and a really busy start to the year, every week I feel like my game is getting better. It has all come together and I just played consistently the whole week," Dryland said.
"It was pretty solid today. After six holes we got told to hurry up and I lost a bit of momentum with a bogey on seven. But it was fine and I came back strong. Mum and Dad live here so it is good to come home and see them and stay with them."
Scores: www.golf.co.nz/Tournaments
