BARCELONA - Barcelona had hoped they had ironed out the defensive weakness that marred their current season but Tuesday's 3-2 Champions League reverse at Paris St Germain appeared to suggest the opposite.

Going into the Group F clash at the Parc des Princes, Barca had yet to concede a goal in seven outings in all competitions but their backline was all too fragile and the Ligue 1 champs took full advantage.

David Luiz, Marco Verratti and Blaise Matuidi all breached the visitors' defence as PSG took early control of the group and handed Barca's new coach Luis Enrique his first competitive reverse since he took over.

Barca's pacy fullbacks, Dani Alves on the right and Jordi Alba on the left, may be dangerous going forward but they often neglect their defensive duties.

Centre backs Javier Mascherano and new signing Jeremy Mathieu, meanwhile, did little to suggest they deserve a regular place in the starting lineup ahead of the likes of Gerard Pique, Thomas Vermaelen and Marc Bartra.

"I am the one mainly responsible for the defeat," Enrique told a news conference.

Captain Andres Iniesta said "it's a team issue, not one of the defensive line, the midfielders or the attack".

While their defence is an obvious cause for concern, Barca's attack has been firing on all cylinders, with Lionel Messi and Neymar in prolific form and each scoring in Paris.