I think the problem we saw yesterday exists in the players heads.  We saw it on Wednesday evening as well.
The team isn't playing well at the moment.  It happens to all teams. So the players feel under pressure to do better.  And in trying too hard to do that, they snatch at chances or make rash passes or tackles.
Funes Mori was the most obvious offender last week.  But there were others.  Some of them let the tension get to them and consequently underperform.  Mirallas' disgraceful tackle on Suarez a few seasons ago was another example
Lukaku ran up to that pen yesterday too quickly.  You can see the tension in his shoulders.  Same with the chances he had first half...first touch was too tense.  Relax and play to your potential lad....
I feel that Barkley too is playing as if he's weighed down by expectation.
Why do we not play as well at home?  Could be that the expectation of the crowd - fuelled by decades of underachievement - communicates to the players.
All of which is not unusual.  All elite sportsmen and women have to live with that.  But it's the coaches job to protect them and teach them how to perform under pressure.
Clive Woodward used a well known little acronym to help England players to win the Rugby World Cup.  T-Cup:  Think Correctly Under Pressure.
How did he give that to the players?  My understanding is that it was practice, practice, practice.  So that; when the crucial moment came in a match such as a key scrum (or a penalty in a football game), the players could relax and treat it like a training session, shutting out the noise and anxiety of the fans and focussing on the task.
When we lost top Lpool in the 2012 semi, I bemoaned David Moyes' unwillingness to let the players express themselves, so they went into the second half riddled with anxiety and handed the initiative back the enemy.  And lost.
Yesterday was different in that we played poorly in the first half and only turned up for the second 45.  All in the players minds.
Not sure what our current coach does with the players to get their heads in the right place.  But I think that's the source of our current malaise.
I'm not a 'Sack Martinez' camp follower.  I felt at the start of this season that he was a man with a plan.  Still think so now.  But he needs to get to grips with this issue and get them playing to their potential.