The Blues claimed a narrow win over their guests after going down one man early on.
Chelsea manager Thomas Tuchel has admitted his team is yet to reach its peak defensive form.
A difficult first half saw the Blues losing Conor Gallagher with a straight red card.
However, Raheem Sterling‘s brace in the second period earned the victory for the Blues in the second period. Despite the victory, Tuchel didn’t shy away from voicing his frustration with Chelsea’s backline.
“Today he is responsible for what he did, and he knows it was a huge mistake,” Tuchel said of Gallagher’s mistake. “We spoke briefly after the game, and things like this happen.
“It’s not purely his fault alone because it was a set-piece for us and it’s sloppy how we take set-pieces at the moment.
“We lack belief and precision, so it’s not good enough. We give chances away, we are sloppy in the coverage and bad in decision-making, so we have to stop and improve immediately.
“We are on it with the team, so I don’t know why it happened again. It’s a very bad decision for Conor, so of course he’s upset, because it almost kills a whole football match.”
The Blues will meet Southampton in a mid-week match this Tuesday.