"It was all down to fitness. I've done over 300 training sessions during the last 90 days. I was able to keep fighting every round and those upper cuts landed a treat," the 27-year-old fighter observed.
"I had so many nerves tonight. But after the first round I thought 'I can do this'. I was waiting for Gunnar to turn it up but I forced myself to turn it up."
While one judge scored the fight 95-all, another scored it 96-94 in O'Brien's favour.
With his win against 32-year-old Jackson, who came to the Bay with a record of 27 wins - 12 by knockout - 11 losses and four draws, O'Brien can expect plenty of opportunities on the Asian and American circuits in the future. However, he refused to look that far ahead.
"I've had three fights this year and I've won all three. I need a break. So I will have the rest of the year off and come back fresh in the New Year and then decide what I'm going to do," O'Brien said.
As clubmates, supporters and sponsors were congratulating O'Brien on his titles and the third child on the way, the couple worked out that the child must have been conceived on his and Lisa's wedding night back in August.
"Yes that was a good night too ... just like this one," O'Brien said with a grin.
"I know boxers who pray for wins. I don't worry too much about wins and losses ... I just pray to make sure I get home safe for the family," he added.
O'Brien's Napier Boxing Club clubmate and fellow professional Toa Leutele captured the vacant heavyweight titles from the same two organisations as O'Brien got his belts, but it was via an anti-climax.
Leutele, 24, was originally scheduled to fight Wellingtonian Cory Enoka but after weighing in on Friday night, he contacted event promoter Scotty Thomson at midday on Saturday to withdraw from the bout.
"Cory told me he couldn't sleep and his head wasn't in the fight," Thomson recalled.
Another Wellingtonian, light heavyweight Thomas Russell, drove up from Wellington to take on Leutele. He arrived at the arena 30 minutes before the fight and was knocked out by Leutele in the second round of their bout, which was scheduled for eight three-minute rounds.
It was the third time Russell had hit the canvas in the round.
These two fights were the first international professional boxing title bouts to be staged in Hawke's Bay. In addition, nine corporate bouts were staged.
Results were: Lana McCarthy (Palmerston North) b Ripeka Dwyer (Highlander Boxing, Napier) by RSC; Kelly Brock (Gisborne) b Kate Hatton (Napier Boxing) by points decision; Paraire King (Palmerston North) b Callum Aldiss (Wellington) by points decision; Stacey Loye (The Lab, Napier) b Nina Houston (Napier Boxing) by RSC; Tabai Tumanako (Wellington) b Dom Leiataua (Highlander Boxing, Napier) by points decision; Tania Barnett (Palmerston North) b Miriata Callaghan (Gisborne) by points decision; Elliot Sharp (Wellington) b Nathan Birch (Tauranga) by points decision; Gerhardt Van Vuuren (Wellington) b Tommy Harrison (Napier Boxing) by points decision; Charlie Rudd (Wellington) b Junior Alivale (Highlander Boxing, Napier).
