Neither Manchester United nor Everton supporters are particularly happy with their managers or style of play at the moment, though the most noticeable difference between the sides lining up at Wembley on Saturday afternoon is Louis van Gaal at least is happy with his team’s defensive record.

While United have been widely criticised for a lack of urgency and invention going forward, a less trumpeted story has been their efficiency at the back. Only Tottenham have conceded fewer league goals and United top the charts for clean sheets with 17, meaning the defence have kept opponents at bay in just over half the team’s fixtures.

Everton, as their league position suggests, are in the bottom half of the table for defending. They have yet to reach double figures for clean sheets, are ahead only of Bournemouth and the relegation candidates in terms of goals conceded, and lost another couple of key defenders in Wednesday’s abysmal showing in the Merseyside derby.

It looks very much as if Roberto Martínez’s famous quote about being more interested in outscoring the opposition than setting up a team to keep clean sheets is going to come back to haunt him and even Van Gaal’s many detractors must grudgingly admit he has got half the equation right, even if a lot of the credit is owed to David de Gea’s excellence in goal.

“Our record shows we have good defensive organisation and that is an important part of playing football,” Van Gaal said. “When you analyse a performance you have to split the game up into different phases: possession, the time when your opponent has possession, and the transition in between. I think we are doing great when the opponent has the ball; that part of our game is working well. Where we need to improve is when we have the ball. I think we ought to be doing better in terms of creativity.”

Everton at their best are a mirror image of that notion, free-scoring and creative but constantly being held back by defensive lapses and an inability to hold on when games appear to have been won. That should make the FA Cup semi-final an interesting contest, though Everton are very far from their best. Martínez’s honest assessment of the worst derby performance most people can remember – “horrible, disastrous” – was formed on the Everton showing before Ramiro Funes Mori had picked up his red card or John Stones and Gareth Barry had left the field injured. It is fair to say any confidence Everton had on winning through to the final has all but evaporated in the past few weeks.

Van Gaal insists there is still no room for complacency. “Everton will not be a piece of cake, even if they did just lose 4-0,” he said. “One thing that can happen when a team have a bad performance is that they fight back in the next match. We did exactly that in the first half of the season when we lost 3-0 at Arsenal. It was a big defeat but in the next match we won 3-0 with one of our best performances of the season.”

That match was at Goodison Park, one of the first signs that Everton’s early season optimism after wins against Southampton and Chelsea might be misplaced. “In spite of them having a lot of injuries, they still have the chance to beat us,” Van Gaal said. “When we played West Ham in the quarter-final it was straight after losing 2-0 at Anfield in the Europa League. We had to recover quickly but we drew 1-1 then won the replay. So Everton can also do that after Liverpool. It is possible, and a semi-final is always difficult to predict.”

One of the scorers in United’s replay win at West Ham was Marcus Rashford, whose seven goals in 13 games have brought him to national attention, even if Roy Hodgson plans to keep faith with Wayne Rooney for the European Championships in summer. Van Gaal intends to stay out of that debate, though he will admit Rashford excites him as a prospect. “He reminds me of Patrick Kluivert at the same age,” he says. “He has the same build as Patrick. Perhaps not quite as developed in body weight and so on but that is just a matter of time. What Kluivert was in my first years at Ajax, Rashford is now. They are very similar players, and they broke through in the same way. Patrick scored the winner in the Super Cup in his first match, and his career took off from there. He did more or less what Rashford is doing now.”

Van Gaal is fond of the FA Cup. Growing up in the Netherlands it was the one live football match shown on television each year. He fully understands his time at Old Trafford will be judged on the final league position but is also aware United have not won the FA Cup in over a decade. “Always when you win a title it represents what Manchester United stands for,” he says. “This club had a period of a lot of titles and we want to bring that back. And when you win the FA Cup, you have a very respectable title, in England more than other countries. In the Netherlands and Spain, the cup is not so highly valued. In Germany they make a bigger event of it and it is even bigger here. When I see people on the streets, they are so excited. I think it would be fantastic for the fans to win the FA Cup. But first we must get past Everton. We are only in the semi-final at the moment, not the final.”