Fletcher led the team out as captain on the night and for much of the evening the Reds seemed on course to book a place in the Capital One Cup final. However, the tie swung back and forth in a dramatic finale at the end of extra time before the disheartening 2-1 defeat in the shoot-out.
"It all seemed to kick off in the last minute of the game," Fletcher told MUTV. "We're really disappointed, we feel we should have got the second goal earlier to kill the tie off. But when you don't do that, Sunderland keep believing and they got their goal, even though we showed character by scoring in the last minute to take it to penalty kicks.
"It is a mental [battle]. The whole game – although I don't think we played well – we dug in and we battled and I really did think we were going to grind it out and go through. But ultimately we haven't done it and penalties are a bit of a lottery... but we should still be disappointed with the execution of our penalty kicks."
Fletcher was United's only scorer from 12 yards as Danny Welbeck and Phil Jones missed the target, while Adnan Januzaj and Rafael had their spot-kicks saved.
"I thought the momentum [from Chicharito's goal] might have taken us through but ultimately it didn't," Fletcher added. "To be out, then to hit Sunderland with a sucker punch, I thought we'd be in the ascendancy going into the