Whanganui struck back before the break after Raukawa grabbed an overthrown lineout ball and stepped through defenders to take off and score a stunning individual try.
But despite narrowing the gap to two points, the hosts could not score in the second half, their best opportunity coming early in the third quarter, but they dropped the ball three times inside the visitor’s attacking 10m.
Having the wind behind them, Horowhenua-Kāpiti made sustained pressure in Whanganui’s half, but could not crack through either, the home side trying their luck with attacking chip kicks behind the defensive line to mixed results.
Whanganui had one last golden chance with an attacking scrum three minutes from fulltime, but a loose pass was claimed by the defenders, who cleared out of their danger zone.
“Overall, pretty proud of the performance, 12-10 is definitely nothing to be disappointed about after one training,” said Whanganui coach Todd Cowan.
“We definitely had our opportunities and probably didn’t take those at times.
“It could have gone either way towards the end, and Horowhenua were lucky enough to get the win.
“Another training will do us wonders this week, so get into another training and then down to Bulls to Wairarapa and Poverty Bay – I think we’ll be fine.”
Horowhenua-Kāpiti U20s 12 (X. Purewai, L. Timms tries; T. Winterburn con) bt Whanganui U20 10 (S. Abernethy, H. Raukawa tries). HT: 12-10.