Ada Matheson travelled to the 1968 Mexico City Olympic Games as a member of the Irish show jumping team with her horse San Pedro, in what proved to be one of the most chaotic episodes in Irish Olympic equestrian history.
Ireland concentrated on the team Nations' Cup competition rather than the individual event in order to protect the horses from competing twice at high altitude. On the final day of the Games, with nearly 100,000 spectators in the Olympic Stadium, a sequence of administrative confusion during the Nations' Cup resulted in Matheson being unable to enter the arena when called - through no fault of her own.
Despite her readiness to compete, she was told San Pedro had been returned to the stables and was then given insufficient time to retrieve and saddle him before the next competitor was called. Ireland's subsequent protests to the Grand Jury and Jury of Appeal, while treated sympathetically, were unsuccessful. Matheson and her horse never jumped a single fence at the Games.