The Saints were on their way to a comfortable win when they went 2-0 up against Leicester City on Saturday.
However, they were pegged back and eventually lost the game 3-2 in the second half.
Post-game, a despondent Harwood-Bellis said: “I can’t really sum up how I’m feeling. It hurts. In the first 15 minutes of the second half, we were still good.
“Conceding three goals in the second half can’t happen. Blaming anyone else is not on the front of my mind.
“Their lad comes on and causes us problems. We don’t deal with him well enough and we get punished.
"I felt we came out in the second half with the same mentality (as the first). They score and then their tails are up.
“Their lad comes on and we concede more. We were defending well but it shouldn’t get to that point.
“I’m struggling to see a positive. It can’t get to us having 10 men and our backs against the wall. I’m struggling to figure out how it can end like that.
“The set-piece at the end, the organisation is not right. People aren’t in positions and we get punished."