Ben Bromley received a 28-day ban following a dramatic finish to the Pertemps Network Handicap Hurdle at Sandown.
The young rider was aboard Nicky Henderson's Call Me Lord and was one of three involved in a titanic tussle in the closing stages of the three-mile contest.
The 4-1 chance edged his way to the lead after two out and although David Maxwell on eventual winner Dolphin Square and Dan Skelton's Wilde About Oscar refused to go away, the nine-year-old appeared to be holding off his rivals.
Bromley and Call Me Lord held the advantage as the trio passed the first of the two winning posts in operation at Sandown and the one used by the chase course. But believing his job was done, the 7lb claimer stood up in his irons in the shadows of the winning post for the hurdles track, allowing Maxwell to steal a nose victory aboard the Philip Hobbs-trained 18-1 shot Dolphin Square.
"He's the toughest little horse that ever looked through a bridle," said the winning rider. "In the whole of the race the only stride he was in front was the last one.
"He's not over big, but he's game. I wanted to be in behind and get a lead, and thought if I was on their coat tails turning in, we would have a chance.
"I thought we'd been beaten a head and can't believe it that we've won. I will only believe it when they give me the champagne."
Call Me Lord was called the runner-up by the judge following a photo finish, with Wilde About Oscar a short-head further back at 20-1.
"It was a stupid mistake and it won't happen again," said Bromley of his mistake, with the stewards handing the rider a ban of 28 days for failing to take all reasonable and permissible measures to obtain the best possible placing on a horse that would have finished first.
To add further salt to the wounds of Bromley, he was also banned a further four days for using his whip above the permitted level from having jumped the second-last.
