When Juan Mata starts, Manchester United invariably win. Simple, really.

The Spaniard’s slipped finish past Willy Caballero on Wednesday night settled the EFL Cup fourth-round tie against rivals Manchester City, adding yet more weight to his popularity at Old Trafford.

A well-timed run and confident stroke into the City net further enhanced Mata’s enviable win percentage under Jose Mourinho.

Now with seven victories from his nine starts - one defeat in that time, at Feyenoord - Mata is a key ingredient.

It is three defeats from five without him in the XI. The scales are tipped.

Favoured within the squad, the 28-year-old is knitting United together in behind Zlatan Ibrahimovic and the one looking most likely to carve open defences.

Mourinho still has decisions to make as to who operates as his No 10 but Mata has staked a bigger claim than most on the evidence so far.

He is gliding through games and so crucial to the way United want to play when they are expected to dominate the ball.

It is why the games Mata has been starting this season have come against the likes of Bournemouth, Hull City and Leicester.

He was left out for the bigger fixtures against Chelsea, Liverpool and last month’s derby defeat, with Mourinho desperate for additional defensive protection and speed on the break.

The Portuguese has not always had either of those, however, and will be thinking of deploying Mata more often from here.

He has endured a couple of sticky afternoons so far this season - against Stoke City, particularly - but is largely producing.

And while Pep Guardiola made a number of changes for the cup clash, Mourinho will have been encouraged at the amount of possession United kept.

That figure stood at 48 per cent, indicating United should perhaps be approaching these games differently.

Mourinho boasts individuals who are capable of controlling games - especially in front of a baying home crowd - and the shimmering Mata is one of them.

His attitude is exemplary too.

“From the first minute until the last, we left everything on the pitch,’ he said stood next to compatriot Ander Herrera on Wednesday.

“We knew we had to be strong in our minds to face this game and I think we were that. We showed today that we're still competing.

“I think it was very important to win after the defeat we had in London. It was a massive game for us, a derby, and it's always difficult to play against Manchester City as they play very good football.

“We gave one hundred per cent and we won today. We need to leave everything on the pitch every single game to win.”

He and Herrera do that and are linking up with each other nicely, but the criticism of Mata is that he does not last for a full 90 minutes.

He has finished a game just once under Mourinho and was spared by Louis van Gaal on more than a few occasions last term.

Perhaps that is in the new manager’s thinking, but Mata’s performances have made him sit up and take notice.

For someone so small, that he is willing to take games by the scruff of the neck is laudable and - while United figure themselves out with a new coaching team - vitally important.

His relationship with Mourinho had threatened to become a sideshow to the club in the early weeks of the season after the well-documented exit from Chelsea.

Mourinho addressed that last month. “I did not want to sell,” he said. “The football we want to play here is different. I think Mata is very adept to do that with his qualities. We need players with these qualities. He has found a very good natural habitat.”

Clever he came out with that line, relatively unprompted, in the weeks approaching trips to Liverpool and Chelsea. Mourinho was not then questioned why he had dropped Mata for those.

Maybe Mata will start being handed the chance to impress when it really matters. After all, United do win when he starts.