Having been second best for much of the game, North End suddenly drew level when Ivar Ingimarsson apparently knocked the ball into his own net, while trying to deal with a Chris Sedgwick cross on 53 minutes.
Coppell said: "The goal from our point of view was just a farce, but it gave them a massive incentive and drive. Their energy levels really raised.
"As for the second goal, we have scored enough goals from corners this year. We know the lessons. It was another bad goal as far as we were concerned.
"After that, we restored our rhythm and had some great opportunities, but it wasn't to be at the end of 90-odd minutes.
"We are frustrated with the world and the reality is we got a brilliant opportunity to get a point or points. We can only blame ourselves. We have no excuses other than our own frailty.
"The longer you are in the game, you realise your opportunities. This was an opportunity for us that we didn't take. I'm not blaming anyone, it happens.
"I thought we lost our thread a little bit and got a little bit anxious. It wasn't all about one team today, Preston hung in when we were going well and defended brilliantly at the end.
"We have played a lot worse this year and won games.
"We created a lot of opportunities, hit the woodwork two or three times and the goalie made a couple of great saves. But at the end of it we have come away with nothing."
Preston were looking to put things right again following a four-match losing streak before the International break.
After a slow start, Sean St Leger made a clumsy challenge on Noel Hunt and Stephen Hunt promptly tucked away a 27th-minute penalty.
Reading were giving Preston the run-around before the bizarre own goal seemed to bring the home side to life.
Then Preston grabbed all three points as Ross Wallace's cross was bundled in from five yards out eight minutes from normal time.
The scorer was 24-year-old Stephen Elliott who was making his first start since joining Preston from Wolves. But in a frantic finish the result, in reality, could have gone either way with chances going amiss at either end.
In the end Preston manager Alan Irvine was happy that the training ground homework had paid off.
He said: "It was important for us that we match Reading in all the qualities they have got.
"They have very good players, they work incredibly hard and play at a really high tempo. They can blow teams away.
"We have worked hard in the last two weeks which has been an opportunity for us to get back to things that we have done well in the past. If that means that has got us a result then it's fantastic.
"I felt we had lost a little bit of an edge in the previous games, nothing major, but in this division it is enough to make a difference between winning and losing because the margins are so fine in all the games.
"I said to the lads at half-time that we were still in the game and it was important for the next 15 minutes that it remained that way. It was important that we didn't fall further behind.
"I felt we would get some more chances. We had had a few in the first half and almost scored. Fortunately it worked out that way for us.
"Conceding a penalty was a big disappointment for us. Reading's own-goal certainly gave us the belief that we could go on and get something more.
"I thought both goalkeepers made a couple of outstanding saves. It was great for Andy Lonergan - he has had a bit of criticism recently.
"The only time Reading managed to score against us today was from the penalty.
"It was a fantastic day for Stephen Elliott. He turned clearances into passes, ran the ball well and held the ball really well.
"He has had to be really patient to get his chance and I am delighted he has managed to take his chance today."