Mitchell gave Palace the lead with a fine drilled finish across goal after being slipped through by Jean-Philippe Mateta, ten minutes before half-time.
But the home side levelled through Emanuel Emegha and found their winner with 13 minutes remaining when Samir el Mourabet tapped-in after Julio Enciso's free-kick hit the woodwork.
Despite a second league phase defeat, Mitchell said Palace remain confident they can go deep in the competition and believes the game could have easily ended differently, had that elusive second goal arrived.
And the wing-back also wants to keep improving in front of goal after getting his second of the season in all competitions.
"It [scoring] is something that I've been trying to work on," Mitchell told TNT Sports. It's something that I think this season I got a bit better at, so I'm happy that I contributed, but unfortunately we didn't take away three points.
"It's disappointing. We created some decent chances. The two open goals were great chances.
"We just have to be more clinical. I think if we score that second goal, we then take away three points."
"We know in every game that we'll get chances. In every game, we believe we can win the match. So we step onto the pitch knowing that we can take away three points from any team, but today it didn't happen."