The Clarets lost the game 2-0, following goals by Aruna Dindane and Herman Hreidarsson.
“The defeat is a big disappointment for me after how well we played,” said Coyle.
“We created numerous chances and we really had to take one of those and, if we had, I’ve got no doubts we would have won the game.
“We have dominated the game, but lost and we cannot keep playing well and getting results like this.
“We carved them open numerous times through good football, but at this level you have to be clinical.
“They (Portsmouth) certainly were today because I can’t remember too many times they got in behind us.
“These are the margins and if you don’t take your chances you are going to be punished.
“At the end of the day it’s another game away from home that we have lost and that adds fuel to the fire – and rightly so.
“We are in the best league in the world and we have made a rod for our own back. But the only way to solve it is through hard work and by keep giving the level of performances we have, but finishing the chances.”
