I said ahead of the game that I wanted Bellerin at RB and Chambers at CB. It was clear as day after 10 minutes that Chambers was going to have a difficult time with Montero - and Wenger did nothing. One thing we know for certain about Bellerin is that the boy has both quickness and pace. That is what was needed against Montero today.
I don't blame Chambers at all for not being able to keep up with Montero, and I don't blame Monreal for being short and weak and not being able to properly challenge Gomis in the air. Wenger had the option to play Bellerin and Chambers in their right positions from the start, but chose the experience of Monreal instead despite his shortcomings at CB. Wenger saw Chambers being taken to the cleaners time and time again, and still had the possibility to solve the situation mid-game - he did nothing. Poor team selection, and poor in game management from Wenger is where I mainly lay the blame for this loss.
However, Chambers got PLENTY of help from Chamberlain today. Still, he didn't position himself a single time to make Montero go inside towards the helping Chamberlain, but instead he time and again left space for him to go on the outside. I may be wrong, but I can't think of a single time when Montero tried to go on the inside. Despite having a distinct disadvantage against Montero to begin with, Chambers handled the situation in the worst possible way tactically.