So You Think held off Snow Fairy in the Irish Champion Stakes at Leopardstown for a third Group One success of 2011.
Sent off the 1-4 favourite under Seamie Heffernan, he had to work hard before getting the better of 6-1 shot Snow Fairy, with Famous Name in third.
The Australian import, who joined Aidan O'Brien's Ballydoyle team in January, won the Coral-Eclipse and Tattersalls Gold Cup earlier in the season.
Meanwhile, Dream Ahead triumphed in the Betfred Sprint Cup at Haydock.
So You Think, a dual Cox Plate winner in Australia, was giving O'Brien a sixth Irish Champion Stakes win in nine years after his sire High Chaparral (2003), Oratorio (2005), Dylan Thomas (2006, 2007) and Cape Blanco (2010).
The winner's stablemate Roderic O'Connor made the early running but So You Think and dual Oaks victor Snow Fairy were well in touch.
So You Think made his move as they turned for home, taking the lead with two furlongs to go and holding off the strong challenge of Snow Fairy, ridden by Frankie Dettori.
SO YOU THINK FACTFILE
- Group One wins:
- Prize money:
The Prix de l'Arc de Triomphe at Longchamp on 2 October or Champions Day at Ascot on 15 October could be next on the agenda for the winner.
So You Think runs for Coolmore and John Magnier, head of the Irish breeding operation, said: "This horse's record is there for everyone to see. He's the kind of a horse who we are spoilt for choice with options.
"He could run in the mile race at Ascot [Queen Elizabeth II Stakes], the mile-and-a-quarter race [Champion Stakes, Ascot], or he could run in the Arc."
Of a potential return to his native Australia, Magnier added: "You could never say never, but it's not imminent."
At Haydock, 4-1 favourite
trained by David Simcock, emerged victorious in a photo finish to win the Betfred Sprint Cup.
William Buick's mount, who had won the July Cup at Newmarket under Hayley Turner, had disappointed in France last time out.
This time the three-year-old went into the lead into the final furlong but started to hang as the line approached.
But he managed to get the better of Bated Breath by a nose with Hoof It another head away in third.
Although a stewards' inquiry was called, the result was unaltered.