To emphasize, Barzagli played as RB until Son created the first chance and that was due to bad positioning from both Barzagli and Douglas Costa. We changed shape to a back 3 and it didn't help either as Douglas Costa does not have the qualities of Cuadrado to fill that position.
@Osman I am not usually one who argues about football tactics and shape but on this matter I am willing to argue forever because I am sure we played a back 3 from Son's first danger up until Lichtsteiner came in. It was as clear as daylight. Your problem in not seeing it is because you were busy counting the number of interceptions Matuidi is making

and he was terrible in that matter as well, I think he succeeded in two or three at most.