For me it was quite obvious we needed to stiffen up on our left and I think the first substitution we made worsened the situation.
We're 2-0 up, Silva was starting to fade and Kolorov was leaving us exposed down the left everytime he ventured forward meaning Mangala was constantly out of position trying to cover for him and Fernando was out of position covering for Mangala. What we should have done is rested Silva, brought Jimmy out left when Jovetic came on and pushed Nasri inside.
At the very least we should have taken Silva/Nasri off brought Clichy on and pushed Kolorov further forward where he couldn't cause as much damage to our defence as he was doing. Kolorov needed protecting from his shit passing, lack of stamina and fitness and as one previous poster said everyone was commenting on it, so if we could all see it why couldn't the coaching staff?
I have a suspicion that because we were at home, on a 9 match unbeaten run and had scored 3 in our 2 previous matches that we were a little guilty of underestimating Burnley and paid the price. The complacency warning signs were there from the 2nd half away to WBA.