Luciano had the ball in the net for Fluminense six minutes from time but the goal was correctly chalked off for offside.
Former Brazil full back Michel Bastos hit the post 34 minutes into the first half for Sport and Marcos Junior came close for Fluminense with an overhead kick but there was little else to trouble either keeper.
Sport now lie one place and two points above the relegation zone with five games remaining. Fluminense are 10th.
(Reporting by Andrew Downie; Editing by Ian Ransom)
