Circus Maximus (10/1) became the first horse since Dawn Approach (2013) to run in the 12-furlong Investec Derby before winning the £538,750 G1 St James's Palace Stakes over a mile at Royal Ascot on Tuesday.
Circus Maximus wins the St James's Palace Stakes as the rain comes down, photo Liesl King
Supplemented at a cost of £45,000, Circus Maximus, trained by Aidan O'Brien and Ryan Moore, held on gamely in the closing stages of the mile contest to score by a neck, denying the fast-finishing King Of Comedy (4/1), trained by John Gosden, in second.
Too Darn Hot, the 2/1 favourite and also trained by Gosden, was a further three-quarters of a length back in third.
Circus Maximus was a creditable sixth in the 12-furlong Investec Derby at Epsom Downs on June 1, but the drop back to a mile and the addition of blinkers proved the right combination this afternoon.
O'Brien was registering his 67th winner at the Royal Meeting and a 30.62/1 double today following Arizona's win in the G2 Coventry Stakes.
This was also the master of Ballydoyle's eighth win in the G1 St James's Palace Stakes and first since Gleneagles in 2015.
O'Brien said: "Maria (Niarchos-Gouaze), Derrick Smith, John Magnier and Michael Tabor [owners] all decided at 11.45am at the six-day stage that they were going to supplement Circus Maximus for this race and we just ran with it.
"It is hard to believe, but we are just privileged to be a small part of it.
"It is a big challenge for the horse to drop back down in trip. That's why we put the blinkers on him as he didn't have much time to learn how to race back at a mile, so that helped him.
"We were worried about the pace of the race for Circus Maximus back over a mile having raced over a mile and a half, so we are delighted really."
It was previously Good on the Straight course and Good, Good to Soft in places on the Round course.
Circus Maximus's 10/1 victory in the G1 £538,750 St James's Palace Stakes handed jockey Ryan Moore a 55th Royal Ascot winner. It was his second success in the race - he took it in 2015 on Gleneagles, again for today's winning trainer, Aidan O'Brien.
The Galileo colt was supplemented for the race at a cost of £45,000 six days ago. He finished sixth in the G1 Derby at Epsom when ridden by Frankie Dettori.
Ryan Moore retuns on Circus Maximus, photo Liesl King
Moore, for whom this was a 30.62/1 double - he won the Coventry Stakes aboard Arizona earlier in the afternoon - said: "Circus Maximus has plenty of speed. The mare [Duntle, Circus Maximus's dam] was good and won a couple of races here.
"Circus Maximus has been a little bit slow coming to himself and learning about it all.
"He showed plenty at two and ran a good race at Doncaster at the end of the year, which gave him a chance, plus the rain helped.
"When Too Darn Hot got to me, he did not go by me, and I knew this horse would keep going.
"Fair play to Aidan because he phoned me up on Monday morning to speak about putting him in the race and I said, 'when you supplement them, they have to win!'
"Aidan knew this horse had a bit of talent and he ran a good race in the Derby, but he didn't stay."
King Of Comedy, sent off at 4/1, and Too Darn Hot, 2/1 favourite, came home a neck second and three quarters of a length third in the £538,750 G1 St James's Palace Stakes over a mile during Royal Ascot's first day.
John Gosden, who trains both the colts in Newmarket, commented: "One ran out of track and the other found that it was a little too stiff a mile.
"King Of Comedy just ran out of track and he ran a blinder. He needed another 25 yards. He is a horse that in the end will go a mile and a quarter.
"Adam (Kirby) said it was a pity he had to come round and through them."
He went on to speak of the third Too Darn Hot, saying: "Too Darn Hot has run a very good race. He has come to win his race, got in front.
"It is just stamina. It wasn't for him today. It is a stiff mile here and it just caught him out. He is a very powerfully built horse - he looks like a sprinter/miler. Frankie said he feels like a Jersey (7f) horse, and that is what he is. He was a champion two-year-old, who won the Dewhurst in great style.
"He needs seven furlongs or an easy mile. The G1 Sussex Stakes (mile, Goodwood, Wed, July 31.) will be next for him."
His rider Frankie Dettori added: "He ran a good race. He came there to win, but perhaps the stiff mile was too far for him."
4.20pm St James's Palace Stakes (Group 1), 1m round
1 Circus Maximus (Flaxman Stables/Sue Magnier/Tabor/Smith) Aidan O'Brien IRE 3-9-00 Ryan Moore 10/1
2 King Of Comedy (Lady Bamford) John Gosden 3-9-00 Adam Kirby 4/1
3 Too Darn Hot (Lord Lloyd-Webber) John Gosden 3-9-00 Frankie Dettori 2/1 fav
Time: 1m 39.9s
Distances: nk, ¾
Tote Win: £12.05 Places: £3.25, £1.70, £1.30 Exacta: £58.50
Breeding: b c Galileo (IRE) - Duntle (IRE) (Danehill Dancer (IRE))
Breeder: Flaxman Stables Ireland Ltd
Aidan O'Brien - 67th Royal Ascot winner
Ryan Moore - 55th Royal Ascot winner