Fields Of Athenry was cut to 10-1 from 14s by the sponsors for the Ladbrokes St Leger after winning the Ballyroan Stakes at Leopardstown in fine style.
Aidan O'Brien's Galileo colt made it three wins from four outings this season, making most of the running under Seamie Heffernan in the Group Three.
Roheryn set out to make all but after a couple of furlongs Heffernan felt the pace was not strong enough and let his mount stride into a clear advantage.
After giving him a breather rounding the turn for home, Fields Of Athenry quickened up smartly to maintain his clear advantage and the 8-15 favourite, despite showing the odd wayward tendency, kept up to his work to beat Edelpour by a length and three-quarters.
Paddy Power make him one of their three 10-1 co-favourites for the Ebor at York later this month.
Speaking in his father’s absence, Joseph O’Brien said: “He’s a lovely horse and stays well.
“Dad was saying that he’ll more than likely go to York for either the Ebor or Voltigeur on his way to the Leger.
“He’s done nothing but improve all year in fairness to him. He’s a nice horse with a big engine.”
Heffernan said: “I would have been disappointed if he had been beaten. An extra two furlongs might play up to his strengths again.
“I wanted to wait to get well into the straight before going for him and had hoped something would be at my boot but I didn’t want to wait too long.
“He’s very genuine and that’s his big plus.”
Joseph was in the saddle himself for O’Brien’s two earlier winners.
Lieutenant General landed odds of 4-5 in the Irish Stallion Farms European Breeders Fund Maiden with the pilot saying: “I would be disappointed if he didn’t pick up a group race on the way, and he could be more. I think he will progress.”
The Crewmaster also did the business for favourite backers at 4-6 in the Bulmers Live At Leopardstown Maiden while later on Ivanovich Gorbatov (11-4 favourite), made it four on the night for the Ballydoyle handler in the Racecourse Of The Year Handicap.
A great night for Ballydoyle was completed when Hallmark (3-1 joint-favourite) made it a five-timer in the hands of O’Brien junior in the Live At Leopardstown Maiden.