The Senegalese shot-stopper made his way up to the opposition box for a stoppage-time corner with his team 2-1 down, and managed to send a brilliant looping header over his opposing No.1.
Championship side QPR had found themselves 2-0 down away to newly promoted Sunderland at half-time, but young Moroccan star Ilias Chair halved the deficit with three minutes of normal time to play.
Then, in added time, the 24-year-old was given another chance to influence the game from the corner flag, with an extra teammate to search for in the box.
Chair's first cross was nearly met by Dieng, Black Cats keeper Anthony Patterson clearing the ball at the second attempt.
However, his punch fell straight to danger man Chair, who again found his man, directing it onto the head of Dieng to take a point.
That wasn't all from the scoring goalie, though, as he still had time to make a point-rescuing save.
QPR manager and former assistant of Steven Gerrard, Michael Beale, spoke to talkSPORT post-match about the incredible scenes.
He said: "We had some honest words at half-time and came out second half and played on the front foot, we lived a little bit dangerously.
"Obviously Ilias scores a good goal and then we have a massive moment with Sinclair Armstrong and I'm thinking that's the moment gone.
"But then Seny had different plans at both ends of the pitch - a great goal followed by a great save."