The promising flyhalf was at the heart of South Africa's attacking moves in their opening game, setting up the first of five team tries and playing an influential hand in several other attacking moves against the powerful England outfit.
Mngomezulu said they are far more settled now that they have one tournament game behind them.
“Now we all know what it's like playing at this level and how small the margins are,” he said, calling for a strong mentality in their second game against Ireland.
“We didn’t play too well but we won by eight points, and we are happy to take that.
“We know what's required of us to do well against Ireland and we are training as if we've lost (our first game). That hunger and desire (to eliminate mistakes) are very evident in our training.”
Mngomezulu expects the wounded Irish to come out firing on all cylinders on Wednesday night, after they lost their opening clash to France by 42-21.
“They must be disappointed with their result against France because they won all their games in the Six Nations, so they would want to rectify matters against us,” said the Junior Bok captain.
“Therefore, we are putting in all the preparations to make sure we are physically and mentally ready to handle them.”
On a personal note, it’s been a memorable season so far for the young flyhalf and he described his involvement in the Vodacom United Rugby Championship with the DHL Stormers as a dream come true.
The Cape franchise won the inaugural Vodacom URC title when they beat the Vodacom Bulls in a thrilling Grand Final two weeks ago.
“As a rugby player, these are the things you work towards and just setting new goals now is the main thing,” said Mngomezulu.
“Whilst I’m with the Junior Boks, my focus is purely on being here and how we can move the team forward and what I can contribute to the team.
“The campaign was an amazing experience, and the lessons I've learnt there is something I want to bring here to help my further development as a player inside a great bunch of Junior Boks.”
The match against Ireland on Wednesday starts at 20h00 and will be live streamed on www.springboks.rugby.