The constant pressure exists because most of the defense and some attacking players don't have the composure and technical ability to keep possession and play the ball out of trouble. There is no change that can be made to address that problem. Bringing on Cahill, for example, would make it worse, not better.
Which players could have done anything about their goal? That's what I'm asking people who think Mourinho was to blame for their goal. The only changes he could have made that would make any difference would be attacking changes. That doesn't suddenly make the back 4 and goalkeeper go from clumsy to composed.
Which would be fine if there were actually other players he could play that would solve those problems. Begovic was terrible for the goal and the corner that gave it away. The three CBs have all been pretty poor this season, and none of them have the technical ability to play out of defense with composure, which just puts them under greater pressure and leads to more mistakes. That's probably why Mourinho wanted to buy Stones in the summer.
How can you when the players have been so bad? It was Begovic's fault that they had a corner in the first place, and have looked like scoring from set pieces all night.