The 22-year-old, whose short but successful career as a jockey yielded Classics on both sides of the Irish Sea and two Irish champion jockey titles, recently announced his retirement from the saddle to concentrate on his training career.
And O’Brien Jnr, who hopes to earn his full training licence in June, could hardly have made a greater impact, inflicting a rare reverse on a Willie Mullins filly at Cheltenham this week, as his horse beat Apple’s Jade in a thrilling finish.
Displaying a confidence beyond his years, and failing to hide the sheer pride and joy, O’Brien Jnr stood tall and positively proudly as he fielded questions from the press in a thronged winner’s enclosure.
“I can’t really put it into words to be honest - it’s unbelievable. It feels slightly surreal,” he said, before assuring “it makes no difference” it is not his name beside the horse’s.
As a son of one of the greatest trainers to ever saddle a thoroughbred, there is an inevitable pressure of expectation but there was little evidence of that in his demeanour or words as he revelled in the occasion.
“I don’t think about things like that too much,” he assured. “You just have to do your best with each horse that comes in. It’s completely different to being in the saddle, though.
“When you’re riding you don’t get a chance to take in the whole occasion, but now, as a trainer, you don’t have much to do on the day itself, as the job is done. It is a completely different feeling - I can’t put it into words really.”
The winner who, like his trainer, enjoyed a Ballydoyle education before moving to Owning Hill, Piltown, looked potentially very smart on debut, but struggled in very testing conditions next time.
Better ground and the value of experience told as he produced a more accomplished round of jumping this time, and travelled with the class of the hundred-plus flat horse he is.
“He was in Ballydoyle on the Flat and was obviously a decent horse,” added O’Brien.
“Then he came to us and has always jumped well. He has been working really well and all the lads at home have been happy - but he was working well before the last day.
“We were very hopeful the ground would make a big different and it has. He is by Montjeu and jumped well from day one, so we always thought he would be nice if he progressed.”
After a long battle to keep his weight low enough to ride on the flat, it was inevitable O’Brien would have to make a difficult decision about his future.
Training, which his mother, father and grandfather have all done successfully, represented a natural progression.
“My weight was a struggle, especially the last year,” he admitted.
“I knew from day one that I would not be able to ride forever and I was very lucky to ride some of the horses I did.
“My (training) course is on in May and hopefully I’ll pass and I’ll be able to go training from there.
"I am hoping to get my licence in June. I have to do the next course because I missed the last one when I was away at the Breeders’ Cup.
“It won’t just be jumpers I’ll be training - it’ll be a 50/50 split between Flat horses and National Hunt horses, about 70 in all. I’ve got a nice bunch of 15 to 20 two-year-olds so I’m looking forward to that.”
Most young trainers would not be positioned to know whether or not they might have a Champion Hurdle horse in their care, but a life around some of the finest thoroughbreds in both codes puts the youngster on a very sound footing, as his proud father assured.
“From the time he has been a baby he has been looking out the back of the jeep watching Istabraq work,” said O’Brien Snr, who trained the former superstar to win at four consecutive Festivals.
“Tommy Murphy used to sit behind me in the jeep and hold onto Joseph so he wouldn’t fall out the window.
"That’s the way it was. He has never known anything else. It’s amazing. But we must remember he is only 22.”
Winning owner JP McManus asked, rhetorically: “It was a team effort but Joseph, how good could he be?”
To students of horse racing, pedigree is key.
The career is still in its infancy but when, eventually, the name JP O’Brien appears in bold print beside a horse, we will all know for sure it could hardly be in better hands.