Rekindling finished with a flourish to lift the Comer Group International Curragh Cup.
Winner of the Ballysax Stakes at Leopardstown in the spring before finishing fourth in the Dante at York, Joseph O'Brien's colt failed to make an impact in the Epsom Derby.
Stepping up in trip but coming down in grade for this Group Two affair, Rekindling was a 6-1 shot under Wayne Lordan.
Favourite Wicklow Brave, last year's Irish St Leger winner, looked home for all money after going clear in the final furlong, but Lordan coaxed a late rattle out of Rekindling and he got up to score by half a length.
Elidor was best of the rest in third.
O'Brien said: "He gave him a great ride and he settled well. He had a little bit of class and there was a chance he would be a little bit better than them.
"Obviously Wicklow Brave is a very good horse, but he had a little bit of class and it worked today. Three-year-olds have a good record in this race.
"It looked today like he could be a Leger horse. He did well to go and get Wicklow Brave, he's a very good horse.
"We hadn't thought much further than today. We were probably finding out about him trip-wise today.
"There is Doncaster and the Irish Leger. He has to go to one or the other and he probably has to go somewhere between now and then as well.
"An awful lot will depend on how the races are looking closer to the time. I'm sure there will be a few better three-year-olds than were taking him on today in Doncaster.
"We'll see what happens closer to the time, but it's nice that he's back in form anyway.
"We'll probably have to meet Order Of St George somewhere. If we don't meet him in the trial here, we might end up meeting him in September here.
"A lot of people are knocking the three-year-old generation, but it will be interesting to see in the next month or six weeks."