Sir Erec has been a short-priced favourite after winning both his starts over obstacles so far, although he has been the subject of a slight injury scare in recent days.
"Sir Erec had a stone bruise earlier this week, but we are confident that he will recover and be fine for the race," O'Brien said. "Sir Erec was very impressive at Leopardstown last time. He jumped very well and whilst he did have the run of the race, we were still delighted with his performance.
"He has a great attitude and has adapted to hurdling very well this term. He was a very good Flat horse and we're looking forward to running him.
"Sir Erec is quite versatile in terms of the ground. He has form on soft ground on the Flat and if the rain continued to fall, that would not be too much of an issue for him.
"I think the Triumph Hurdle is a very competitive race and there are any number of horses who could put it up to him. He's in good shape and we wouldn't swap him for anything."
O’Brien has a good back-up team in Fakir D’Oudairies, Band Of Outlaws and Gardens Of Babylon.
Other Irish possibles include six from Gordon Elliott’s yard, of which Surin is a feature, while Tiger Tap Tap is among three trained by Willie Mullins.
The home team is led by Paul Nicholls’ prolific winner Quel Destin. The Ditcheat trainer also has Pic D’Orhy and Ecco.
Nicky Henderson is two-handed with Adjali and Pentland Hills.
The well-fancied Commander Of Fleet, from the Elliott stable, is among 43 remaining entries in the the Albert Bartlett Novices’ Hurdle.
Potential opposition includes Birchdale and Dickie Diver from the Henderson team and the Rebecca Curtis-trained Drovers Lane.
Dan Skelton’s Mohaayed, winner of the 2018 Randox Health County Hurdle, is one of 45 left in this year’s renewal.
Ozzie The Oscar, trained by Philip Hobbs, heads the weights after 41 remained in the Johnny Henderson Grand Annual Challenge Cup Handicap Chase, for which the Nicholls-trained Magic Saint has headed the ante-post betting.
Elliott’s Dallas Des Pictons and Uradel from the Mullins stable are big names among a list of 65 left in the Martin Pipe Conditional Jockeys’ Handicap Hurdle.
The St James’s Place Foxhunter Challenge Cup has attracted 26 possibles, including the Nicholls-trained Pacha Du Polder, winner for the last two years.