Ireland's David Simpson cleared a height of 2.20m (7ft 3in) on Richi Rich to win the puissance at the London International Horse Show at Olympia.
Simpson beat Karline de Brabander of Belgium, riding Fantomas de Muze, in the fifth round to end the event without picking up a penalty point.
Britain's Joseph Clayton finished third on Rockim, with four penalty points.
Clayton's fellow Britons William Whitaker and Guy Williams were 11th and 12th respectively.
Puissance is a knockout competition in which 12 riders try to jump over a wall which starts at 1.8m (6ft) tall and grows with each round.
The year-ending Olympia event runs until Monday.