Capri gave Ryan Moore a first victory in the William Hill St Leger as Aidan O'Brien's grey held Crystal Ocean in the world's oldest Classic at Doncaster.
The son of Galileo became the first horse since Triple Crown hero Nijinsky in 1970 to win both the Irish Derby and the St Leger, in his first race since his success at the Curragh 77 days earlier.
Sky Bet reacted by cutting Capri to 9/1 in their non-runner, no-bet market for the Prix de l'Arc de Triomphe on October 1.
The Anvil soon established a big lead from his three O'Brien-trained stablemates, led by Douglas Macarthur with Venice Beach and Capri just behind. Then there was a gap to John Gosden's duo of Stradivarius and Coronet.
The Anvil was a spent force tuning for home into the long straight, where Douglas Macarthur briefly took over.
Stradivarius looked a real threat on the far rail, but Capri (3/1 favourite) was already close to the pace and set sail for home inside the final quarter-mile.
Crystal Ocean made a strong run from the rear, but Capri held the aces to score by half a length and give O'Brien a fifth win in the race. Stradivarius was just a short-head away in third.Moore said: "He's a very good horse, he's an Irish Derby winner and a Group Two-winning two-year-old as well. He's run in a lot of good races this year, he's a very good horse and very honest.
"When Crystal Ocean came to him, he dug in. He's done very little wrong in his career and has progressed from race to race.
"It was a very good performance in a very good St Leger."
On winning the race for the first time, he told ITV Racing: "It means you have to win it again, really."
O'Brien said: "We were all delighted with him. He had a little blip at York time (when he missed the Great Voltigeur). We were a little worried coming here, but Ryan gave him a class ride.
"All four of the lads were handy and everyone was happy with the pace Michael (Hussey) was going on The Anvil.
"He's a horse with a lot of class, which we saw in the Irish Derby. When Ryan wanted it, he gave it to him.
"Seamus (Heffernan) rides him a lot at home and has always been a big believer in him. He always said he had class and that he would stay.
"Ryan had ridden him once before when winning the Beresford on him, but that was last season. I was a bit worried about that as well, but it all went great."
He added: "As he had a blip at York we were worried coming here, but that he would improve a bit for the run. We had it in our heads that if all went well today and everything went well after he could run in the Arc.
"Obviously the lads (Coolmore) will decide what they want to do - run him again or put him away. He's probably a mile-and-a-half horse with class, so he'd have no problem going a mile and a quarter.
"He has a great cruising speed and we always thought he had courage and stamina as well as class."
Sir Michael Stoute felt Crystal Ocean just found his stamina running out.
He said: "I'd prefer to have won it, but he ran a great race, we're thrilled with him.
"I thought he was going to win, but we won't run him beyond a mile and a half again. It was always a danger that he was a mile-and-a-half horse and that's his trip.
"Jim (Crowley) gave him a lovely ride and I always felt he might win. Jim reported he was always pretty confident, but he was just outstayed."
Gosden said of his two runners: "He (Stradivarius) has run a cracker. It was a relentless pace, very strong and there was no hiding place.
"Coronet has run a lovely race (fifth) and she will go to Champions Day for the Fillies & Mares race.
"This fellow (Stradivarius) got isolated, he was coming back in the last 50 yards but they were racing away from him and he wasn't racing against anything.
"If he comes out of it well he will go to Ascot for the Stayers' race (the Qipco British Champions Long Distance Cup)."