"We feel very much aggrieved," Coppell told Sky Sports News. "Having got ourselves in a good position, my players are adamant the penalty, which changed the game, should never have been.
"Having seen the angle of the referee, he could never have seen whether there was contact on the ball or not
"For us it is disappointing to give away a lead at half-time.
"It is a sign of our progress we have come here and taken part in an entertaining game, but it is disappointing we have come away with nothing.
"It is a massive frustration and disappointment."
Glenn Roeder
Newcastle boss Glenn Roeder was a happy man after seeing £10million signing Obafemi Martins break his Barclays Premiership duck at St James' Park.
The 22-year-old Nigerian converted a 57th-minute penalty to drag his side back on to level terms and set the scene for Emre to win three precious points with a spectacular late strike in a 3-2 victory.
Roeder said: "I could not be more pleased. He certainly showed he knows how to score a penalty.
"It is only a matter of time before he shows everybody he knows how to finish in open play.
"He had a goal taken off him against Portsmouth, which we all know now was a poor decision, and there have been a few incidents recently - he hit the crossbar at Middlesbrough and again tonight with a tremendous header.
"He has just not quite had the breaks he deserves, but it is starting to come and if he can pinch some goals in the next few games, that will give him even more confidence.
"But I am sure the celebration we saw tonight, we will see many more times."
The Magpies lifted themselves into 15th place in the table after a rollercoaster of a game in which they led through Antoine Sibierski's sixth goal of the season.
However, James Harper's late first-half double put the Royals in the driving seat - a point would have put them third - as the home side faltered.
Full-back Celestine Babayaro, who had been at fault for the second goal, suffered the ignominy of being booed by his own fans after the break as the frustration mounted, but Martins' spot-kick and Emre's superb 86th-minute piledriver clinched victory.
Roeder said: "Babayaro showed immense courage and bravery to play through that difficult period.
"I was quite surprised at the reaction he was getting when he was on the ball early in the second half.
"But, typical of our supporters, he kept showing for the ball and playing well and it all changed again and they got very much behind him."
Roeder, who later revealed Emre had been incensed at comments made to him by a member of the Reading coaching staff, was delighted to have collected a second successive league win despite the nailbiting nature of its arrival.
He said: "I suppose, in a strange way, that was the sort of game Newcastle fans enjoy - as long as the outcome is what the outcome was at the end of it."