HSOB were the first to strike when winger Sooga Fa'a'lelei went over for a try in the 17th minute but Ngatapa were quick to regroup and levelled with the first of two tries to halfback and match MVP (most valuable player) Michael Livingston.
The blue and whites regained the lead (8-5) when fullback Cory Reihana kicked a penalty in the 27th minute.
A penalty try to Ngatapa in the 31st put them 12-8 up and they extended their advantage to 19-8 at the break through a try to centre Peter Livingston, converted by first five Ricardo Patricio.
A fired-up HSOB burst out of the gates in the second half with a busting try to hooker Liumai Mokoi and he completed a powerful double soon after.
Reihana's successful conversion put them 20-19 up after 47 minutes.
Ngatapa regrouped and their engine started firing on all cylinders.
Patricio kicked a penalty to push them 22-20 ahead and with momentum on their side, halfback Livingston took the opportunity when it arrived to score his second try and ease the pressure.
Patricio's conversion gave them breathing space at 29-20 and that became a healthy cushion in the 70th minute when replacement Karl Mackie scored to make it 34-20. Ngatapa's strong finish was the difference but HSOB will take motivation from their efforts, noted by co-coach Danny Boyle.
“We were very proud of the performance.” he said. “It was good to have ball in hand — an awesome effort by our boys.
“Our accuracy at the breakdown is probably something we will work on this week.”