Substitute Tyler Burey scored his first senior goal for Millwall as they dealt London rivals QPR's promotion hopes another blow with a 2-0 Championship victory at The Den.
The 21-year-old came off the bench in the first half and it was his fine finish that sealed a second win in a row for Gary Rowett's side, who lifted themselves up to 14th in the league table after Mason Bennett's opener.
QPR were hoping for a reaction to Saturday's shock narrow defeat at Barnsley but they failed to get anything from the game as they remain fourth - six points behind second-placed Bournemouth, having played a game more.