RIO DE JANEIRO, Jan 7 (Reuters) - Reigning champions Flamengo missed a chance to close the gap on Serie A leaders Sao Paulo on Wednesday when they lost a last-minute goal and went down 2-1 to Rio rivals Fluminense.Giorgian De Arrascaeta headed Flamengo 1-0 ahead after 40 minutes when he was first to react to a loose ball in the box, but Luccas Claro equalised 12 minutes into the second period with a deft header.But just as the teams looked set to share the points at an empty Maracana stadium, Fluminense midfielder Yago seized on a loose pass and stabbed the ball into the net.The result leaves Flamengo in joint second place with Atletico Mineiro, seven points behind leaders Sao Paulo.The win snapped a two-game losing streak for Fluminense and they sit in seventh place in the 20-team table.(Reporting by Andrew Downie; Editing by Kenneth Maxwell)