Jockey Kieren Fallon came second in a race he should have won "at a canter", a trial has been told.
Irish-based Fallon is on trial at the Old Bailey
Jonathan Caplan QC, prosecuting, said the champion jockey seemed to stop riding Ballinger Ridge as he entered the home stretch with a huge lead.
A ruling body later found he made an error of judgement in the race at Lingfield in March 2004.
Six defendants at the Old Bailey deny conspiracy to defraud customers of the internet betting exchange Betfair.
'Virtually doing nothing'
Mr Fallon, 42, of Tipperary, Republic of Ireland, told a stewards' inquiry into the race that he had given the horse "a breather", the court was told.
He claimed he was afraid the animal would become "legless" if he kept up the pace, the court heard.
The Jockey Club was not aware of the full picture at the time, Mr Caplan told the court, adding that an expert for the prosecution had since found the ride to be "not a marginal case of a jockey dropping his hands".
The prosecutor told the jury: "He [the expert] notes that passing the two-furlong marker Ballinger Ridge was five or six lengths in front.
"But Fallon then dramatically slows his momentum to the point where he is doing virtually nothing.
"Prior to the one-furlong marker Fallon turns and looks back. The other runners are four to five lengths behind.
"Fallon eases the horse down, which would send the message to the horse that the race was over."
The court was told that the Australian expert had then found Mr Fallon looking round again at the half-furlong, but "only tries to get going again" when another horse, Rye, is going past.
He said: "By that time Ballinger Ridge has lost momentum. There is no legitimate reason that a jockey would need to be looking back and steadying his horse down with a furlong still to go.
"When you look at all the evidence in this case, you can be sure Mr Fallon wanted Rye to be the winner."
Mr Caplan told the court how betting syndicate boss Miles Rodgers, 38, of Silkstone, South Yorkshire, had placed £74,000 on Ballinger Ridge to lose the race.
He alleged that fellow jockey Fergal Lynch, 29, of Boroughbridge, North Yorkshire, acted as an intermediary between Mr Rodgers and Mr Fallon in a conspiracy to make horses lose.
Mr Caplan also said that on the day of the race, Mr Rodgers phoned Mr Lynch nine times before the race and that Mr Lynch sent a text message to Mr Fallon just under two hours prior to the race's start.
Mr Caplan told the court that the Jockey Club called the police after the race in March 2004, and in mid-May, an investigation was started.
Then, on 15 May, Mr Fallon won a race on Russian Rhythm, a horse Mr Rodgers had backed to lose, the jury was told.
Mr Rodgers was angered at the win which cost him £160,000, it was alleged.
The jury was told that after Mr Rodgers was unable to confront Mr Fallon face-to-face, twelve days after the race an undercover policeman saw Mr Rodgers, Mr Lynch's brother, Shaun Lynch, and a man called Philip Sherkle driving towards Mr Fallon's house near Newmarket.
The court also heard that in August a ticket had been bought for Mr Fallon to accompany Mr Lynch and Mr Rodgers on a trip to Spain to meet the "Big Man" in the conspiracy.
Mr Caplan told the jury: "Although Fallon did not join them on the trip to Spain, a ticket for him had, in fact, been purchased by Fergal Lynch.
"The ticket confirmation had been seized after Fallon's arrest from the glove compartment of his car. Fallon was a 'no show' on the flight.
"That trip was made, at least in part, to enable Rodgers and Fergal Lynch to meet with the persons residing in Spain who were parties to this conspiracy."
Mr Fallon, Mr Rodgers and Mr Lynch, as well as Mr Lynch's brother Shaun Lynch, 37, of Londonderry, Northern Ireland, Darren Williams, 29, of Leyburn, North Yorkshire and Philip Sherkle, 42, of Tamworth, Staffordshire, have all pleaded not guilty to being involved in the conspiracy.
Mr Rodgers also denies concealing the proceeds of crime.
Mr Fallon has won six champion jockey titles in the UK and on Sunday he won France's biggest race, the Prix de l'Arc de Triomphe.
The trial continues.