Chris Coleman admits he was "disappointed" in Callum McManaman after the winger saw red in the 3-1 defeat to Reading.
McManaman was given his marching orders three minutes into added-on time at the end of the first half for a second bookable offence after inexplicably putting the ball in the Reading net with his hand at the back post following an Adam Matthews cross.
His moment of madness cost Sunderland dear and Coleman admits his side never recovered from the psychological blow.
Sunderland, down to ten men for the duration of the second half, fell behind to David Edwards' 53rd minute goal before Modou Barrow struck twice in three minutes to seal the win.
Lewis Grabban scored his 11th of the season from the penalty spot 15 minutes from time but it was merely a consolation as Sunderland extended their winless streak at home to 21 games.
"I was a little bit disappointed with Callum," said Coleman.
"I thought he was going to head it. On the re-run there was contact from behind, I don't know whether his hand went up or he was going up with his hand anyway.
"It is hard to see. It is tough for the referee not to if he thinks it is a deliberate handball.
"From thinking we have scored, to then being seconds later down to ten men that was a killer for us psychologically and we never got back from it."
McManaman will now serve a one match ban and miss the trip to league leaders Wolves in the Championship next weekend.
This was Coleman's first home game in charge since taking over from Simon Grayson but the Black Cats were unable to build on the 2-0 win over Burton Albion last weekend.
"Last week was very positive, this week, it is a kick back down into the gutter and we have to deal with that," added the Black Cats boss.
"Between now and the end of the season there are still a lot of games and opportunities here but every game that goes by here when we don't get a magical three points it grows and grows.
"We are the only ones that can stop that and do better. Today that moment when we got Callum sent off was a big moment, a big shift and it cost us."