Kew Gardens gave Aidan O'Brien and Ryan Moore back-to-back victories in the William Hill St Leger at Doncaster.
The 3/1 winner was following in the hoofprints of stablemate Capri and was produced to lead two furlongs from home before staying on strongly all the way to the line.
He had to as 7/4 favourite Lah Ti Dar, who showed signs of greenness through the race, came through to chase him down but she could never land a telling blow and was two-and-a-quarter lengths adrift at the post.
Southern France (20/1), a stablemate of the winner, was a further four-and-a-half lengths away in third.
Moore told ITV Racing: "It was very smooth. He's a very uncomplicated horse and he tries very hard. He's got a great attitude to life and he picked up really well. He's a super horse."
Sky Bet cut the winner to 20/1 from 33s for the Prix de L'Arc de Triomphe at ParisLongchamp next month.
Kew Gardens won the Queen's Vase at Royal Ascot back in June as well as the Grand Prix de Paris in July and O'Brien was delighted to see the Galileo colt add a Classic to his record.
He said: "We couldn't be happier with him. He's a horse that's progressed lovely. We saw what he did in (Ascot) and we were delighted with him in France. We always thought he was a horse that would stay well and we thought the distance would suit him. He has a lot of class and we're over the moon really."
John Gosden was not too disheartened to finish second with Lah Ti Dar, as he felt his filly was caught out by her relative lack of experience.
He said: "She ran a great race and as Frankie said, that's the first real race of her life. She's only ever seen about one horse before today. She was beaten by a proper horse and a proper Leger horse - a Grand Prix de Paris winner and a Queen's Vase winner. She's run an absolute blinder and we're thrilled with her.
"The early pace was a lot slower than we thought it would be. Everyone said 'oh that's good, she'll stay', and I said 'actually I'm not sure it's going to suit her'.
"In the end the best horse won - make no mistake - but I like the way she was closing him down late on. She was getting to him and getting to him. There was a period at the three (furlong marker) where you said 'she's not going to be placed', but then she got balanced and organised. She's never raced against other horses before.
"We'll freshen her up and go for the fillies' and mares' race on Champions Day at Ascot and then put her away for next year. That's the plan."
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