Sent off a 14-1 chance, he was yet another big winner for owners King Power Racing and Andrew Balding who are enjoying a thrilling summer.
They were also on the mark at Ascot with Beat The Bank who won the Summer Mile for a second time and Mystery Power, who took the Superlative Stakes at Newmarket.
Hornby was patient on the five-year-old as Mountain Hunter, Big Kitten and Setting Sail were in a line entering the final furlong.
Pivoine made his challenge widest of all in the centre of the track and he quickened up stylishly to win by a length.
Setting Sail almost defied stall 23 in second while What’s The Story made late headway to claim third and Another Touch was fourth.
Hornby, 24, said: “It was always going too good to be true. He travelled like a dream. It’s important to get him settled early, and he did and got into a lovely rhythm.
“He likes it round here and I just had to wait to press the button as I knew he has a good turn of foot and conditions were perfect today.
“Approaching the last furlong, I thought ‘this can’t be happening’.
“They were coming up the middle all day and that’s great for a horse like him.
“I was able to make ground and get cover which is an important ploy for this horse. It was seen to good effect today.
“It’s huge for me. I started at Mr Balding’s when I was 16 straight from school and all my big successes have been for the Balding family. It’s just been a massive journey through for my career and it’s continuing which is nice.”
Copper Knight earned himself a crack at the best sprinters around when outpointing several notable speedsters in the John Smith’s City Wall Stakes at York.The Tim Easterby-trained five-year-old is now pencilled in for the King George Qatar Stakes at Glorious Goodwood and the Coolmore Nunthorpe Stakes back at the Knavesmire next month after this Listed triumph.
Copper Knight (2-1 favourite) was always close to the frenetic pace set by Caspian Prince before asserting in the final furlong and holding the pack, led by Dark Shot, by half a length under David Allan.
“Brilliant. What a lovely horse he is. He’s been a star for us,” said Easterby.
Allan completed a quick double with a thrilling success on Red Verdon in the John Smith’s Silver Cup.
He gave Ed Dunlop’s six-year-old a patient ride as Weekender and Kelly’s Dino took the field along for the majority of this mile and three-quarters contest.
Escobar could be bound for Goodwood after enjoying a confident ride from Jamie Spencer in the John Smith’s Racing Handicap.
Ten Sovereigns landed a gamble as he registered a stylish success in the Darley July Cup at Newmarket.
He was the subject of some strong support and was sent off a 9-2 chance as Aidan O’Brien and Ryan Moore altered tactics on last year’s Middle Park Stakes winner.
Having run respectably when fifth in the 2000 Guineas, he was ultimately disappointing in the Commonwealth Cup at Royal Ascot when a well-beaten fourth behind Advertise.
Back on a sound surface, the had no trouble in turning that form around as his Ascot conqueror gave vain chase, but could only get within two and three-quarter lengths – despite the best efforts of Frankie Dettori.