Flemming struck a third Premier League goal for the season in Saturday's setback.
The 27-year-old said: "It's a very unnecessary defeat, which makes it even worse for us. We know how strong this league is, but we walk off that pitch today with that feeling inside, knowing that game was there to be won, it's disappointing."
Flemming continued: "Even when they equalised just before half-time, it wasn't a massive killer for us and didn't define the game, we knew that at half-time.
"If you go in at half-time at 1-1 or 2-2, you know the game is still there for either team to win it, but I thought we lacked a bit of our game management really and that's what has cost us in the end."
On his goal, Flemming added: "It was a really nice feeling, putting us 1-0 up away from home and piles the pressure onto them and I think it was a reward for how well we were playing at that time too.
"It was a good team goal, not just the cross and the header, but the build-up and movement from the other guys, so that was a good feeling, but right now it means nothing really."