Donjuan Triumphant, the first horse bought by the late Leicester City chairman Vichai Srivaddhanaprabha, sealed an emotional win in the British Champions Sprint Stakes at Ascot.
Three-time champion jockey Silvestre de Sousa rode the 33-1 outsider to victory in the colours of King Power.
The surprise win came just hours before thousands of Leicester supporters took part in a walk to mark the first anniversary of the helicopter crash which claimed the life of Srivaddhanaprabha, plus four others.
“I wish the chairman could be here, he loved Ascot and having winners here,” De Sousa said.
“I hope that wherever he is he can see this win. It means everything to get one for King Power Racing.”
Magical day as Dettori wins 250th Group One
Elsewhere on Champions Day, evens favourite Magical landed the Champion Stakes, a first for trainer Aidan O’Brien, who claimed a double on Saturday.
And Frankie Dettori won the 250th race of his career at flat racing’s Group One level when Star Catcher (7-4 favourite) triumphed in the Champions Fillies and Mares.
Donjuan Triumphant’s trainer Andrew Balding, who confirmed the horse is to be retired to stud in France, said: “It’s fantastic for King Power, a first Group One winner and this was the first horse the Chairman ever bought so it’s all got symmetry, it’s lovely.
“It was the first horse we had for him (Srivaddhanaprabha) and he would have been so proud of him right now.
“He was a special man with a very generous nature and he’s a huge loss to everyone at Leicester and anyone who knew him.”
Magical, a daughter of super sire Galileo, won for the ninth time in 21 starts over the one mile and two furlongs distance.
O’Brien also triumphed with Kew Gardens (7-2), who won the Long Distance Cup to inflict a first defeat in almost two years on superstar 8-13 favourite Stradivarius, ridden by Dettori.
“She has a great attitude and she’s everything you want in a race horse,” jockey Donnacha O’Brien said of Magical.
The William Haggas-trained Addeybb (5-1) narrowly finished in second in the Champion Stakes, with Japanese challenger Deirdre (10-1) in third.
Jockey Jim Crowley rode Regal Reality to an early lead, which he maintained until just under the two-furlong mark, when Magical moved through.
“She has a great attitude and she’s everything you want in a race horse,” trainer O’Brien, jockey Donnacha’s father, said.
“She’s incredible, unbelievable. She’s an amazing filly. She’s by Galileo, which makes her very special.”
Gosden and Dettori had some consolation for the Stradivarius defeat after Star Catcher edged past Delphinia to win the Champions Fllies and Mares.
Cornelius Lysaght, BBC racing corrrespondent
So Gosden and Dettori continued their prolific season with a favourite taking a prestigious prize on British Champions Day though it was with Star Catcher, battling through a gap some fillies would certainly have declined, rather than one of their principal standard-bearers Stradivarius.
The trainer admitted he came ‘fairly close’ to pulling out the long distance-race champion because of rain-softened going, and is now looking forward to challenging for a third Gold Cup at Royal Ascot in 2020.
Star Catcher gave her jockey a 250th success at Group One-level: aged nearly 49, he’s still gobbling up landmarks.