Just Fine made history as the first winner for King Charles III since he inherited the late Queen’s horses.
The 10-3 shot, who won at Leicester, was the sixth runner to carry the royal purple, red and gold colours since Queen Elizabeth II died on 8 September.
Ryan Moore rode the horse to victory for trainer Sir Michael Stoute in the 10-furlong handicap race at 15:10 BST.
“Their Majesties are thrilled by Just Fine’s success,” said a spokesperson for the King and the Queen Consort.
Just Fine won the £15,000 race by four and a half lengths from the 9-4 favourite Sea The Casper.
Queen Elizabeth II had herself acquired the royal racing colours – purple with gold braid, scarlet sleeves and black cap – from her father King George VI.
“A winner for the King! It is great to have done that for him – and he was very impressive,” said Stoute.
Stoute and Moore combined to give the Queen victory with Estimate in the Gold Cup at Royal Ascot in 2013.
The King’s first runner, Educator, was second at Salisbury on Thursday and while the horses will run in his name, the Queen Consort Camilla is expected to take a keen interest.
“I’m delighted that the King and Queen Consort have had their first winner and they’ll be delighted,” said John Warren, the King’s racing manager.
“I’m also absolutely thrilled for Sir Michael Stoute, who was probably the longest-standing trainer for Her Majesty, and for Ryan Moore, who has put in a big effort as well.
“And for all the team at Sandringham, who rear and go through all the effort to produce the horses all in good shape, so it’s a big commitment on everyone’s part to get a result.”
The King previously had winners in the colours he shared with the Queen Consort when they were the Prince of Wales and Duchess of Cornwall.