He wasn't too slow to get back though, he was back, and got in a good position before the cross, he just didn't watch the scorer as he then let him back in front of him, it was nothing to do with his pace, but his poor defending.
However as I asked last night, where were the 2 CB's in that move, and how did they manage to get the ball through our midfield, from right corner to left corner of the pitch, to Lallana with such ease for the cross, and where was the challenge on the cross ? Kolarovs part in the goal was certainly poor, but most of the team played some part in how crap it was.
We are so easily bypassed at times, that you can almost call a goal when the ball is still in the opposition final third, once we give it away. Its a team thing not an individual thing, yes he should have done better with the pass from Yaya, and certainly with a challenge on the guy who scored, but there is more to it than just Kolarov's input.