SAO PAULO, Dec 13 (Reuters) - Sao Paulo fell to their first Brazilian league defeat in 18 games on Sunday when they lost 1-0 away at arch rivals Corinthians.The league leaders fell behind to a superb first-half shot from Romulo Otero and could not claw back an equaliser at an empty Neo Quimica arena.The result does not change things at the top of the Serie A, where Sao Paulo, who last lost in the league at the start of September, lead Atletico Mineiro by four points and Flamengo, who have a game in hand, by five.The three points lifted Corinthians into ninth place in the 20-team table.(Reporting by Andrew Downie; Editing by Stephen Coates)