Tom Lees bundled in at a first-half corner after Matt Ingram's poor punch served the ball up, and Duane Holmes' brilliant second came when a corner came all the way out to him and the Tigers defenders failed to close him down.
"The goals we conceded disappointed me most," said McCann, who was rightly full of praise for the way his side plugged away. "There's nothing else in the game.
"The first one we should deal with, the second one Duane Holmes we know is right-footed, we let him come inside and it's a great finish but that shouldn't happen. We should be keeping him outside and getting to the ball quicker.
"Before that we had big opportunities, Keane (Lewis-Potter)'s chance where the keeper comes rushing out, crosses into the box, Mallik Wilks) had a chance at the end, huge chances we just didn't take.
"There were 30 crosses in the box and we haven't got on the end of any of them. That's really disappointing for us.
"Between both boxes, I've said it a couple of times this season, the play was good but we have to be more ruthless at this level. When you get big chances you have to take them."
Hull felt hard done-by by referee on Robert Jones for the opening goal, but McCann admitted his side were more to blame for conceding.
"We felt it was a free-kick on Andy Cannon (before the corner)," he said. "We've watched it back and he's got a huge cut down his shin from the tackle. Robert hasn't given it.
"But we should still defend the corner better, down to 10 men or not. I think if you ask Matt Ingram, he would tell you he's got to deal with that better, he's got to punch that."