The Royals crashed to a 3-0 defeat at home, and had striker Pavel Pogrebnyak sent off with 35 minutes remaining.
Wigan's Arouna Kone scored twice in two minutes just before half-time and Maynor Figueroa extended the lead before Reading's Russian striker was shown a straight red card for a foul on the same player.
However McDermott felt an infringement in the lead-up to Kone's first goal, and Phil Dowd's decision to dismiss Pogrebnyak were unjust.
"There was a handball, an absolute nailed-on handball, then their guy headed it in," said McDermott of the first goal.
"The second goal was a poor one from our point of view. They got the third, then Pavel got sent off so obviously it was a bad day.
"With Pavel's sending off, the referee feels it was a poor tackle, that's his decision. Having said that, we have had a bad day, we cannot say that Wigan were not the better side.
"He's made a choice, he thinks it was a dangerous tackle, Pavel's just dangled a leg there and caught him. The referee thinks it was a red card, that it was a dangerous tackle. I know Pavel Pogrebnyak, he is not a dangerous player whatsoever."