Liverpool went ahead through Trey Nyoni and substitute Alexander Isak, but Mason Greenwood and Archie Brown twice brought the hosts level before Vedat Muriqi headed home a late winner.

Iraola identified Liverpool's defending from set-pieces as the main reason for the defeat, admitting his players had failed to deal with a threat they knew Fenerbahce would pose.

"The main reason I can find to lose the game is we conceded from three set-pieces," he said. "It's something that we were doing very well in the league. We knew it was one of the strengths of Fenerbahce, but we conceded from a free-kick, from a corner, even from the long throw at the end."

The Liverpool coach was particularly disappointed because his team had enjoyed good spells of possession and twice taken the lead, only to surrender their advantage.

"It's frustration, because it's a difficult place to come here and to play and we were for the most part of the game thinking, 'OK, we can win this one.' But obviously it hasn't happened," he said.

Iraola also questioned his defenders' organisation for the goals, pointing to mistakes that he believes should have been avoided.

"Especially the first goal and the third goal – the second one is a rebound – but the wall, I don't think we set it properly and the last one Muriqi jumps and wins the ball against three of our defenders," he explained. "It's something that definitely we have to defend better."

He dismissed suggestions that his decision to make five changes to the starting line-up had contributed to the defeat, insisting rotation was necessary because of the demanding fixture schedule. He also defended his decision to play Bradley Barcola through the middle, explaining that the forward's pace and the expected match-ups made him a suitable option.

Iraola insisted the biggest disappointment was how quickly Liverpool conceded after scoring, rather than their overall attacking performance.

"We had, before scoring the goals, some very good moments on the ball. I think we're having very good offensive situations. The thing is we concede almost straight away," he said.

The coach admitted Liverpool had failed to execute their defensive preparations, despite spending considerable time working on set-pieces during pre-season.

"We've reinforced a lot the defensive set-play situation. We are doing very well in the league, but today it has cost us," Iraola added.

Jose Mourinho hails Real Madrid's courage after dramatic AEK Athens comeback