One momentary lapse ruins otherwise perfect Reece James display against Jamie Vardy

Chelsea’s Wembley tracksuits were slightly too informal for some of those watching and Reece James found out the hardest way possible that one casual pass can be oh so costly.

Thomas Tuchel’s surprise decision to switch James and Cesar Azpilicueta, with the 21-year-old playing on the right side of Chelsea’s back three, had worked brilliantly against Leicester City at Wembley for an hour.

But, unfortunately for the Blues and James, one poor ball out from the back was all it took for Youri Tielemans to take advantage. It was Ayoze Perez who got in front of the pass, perhaps with his arm, and the Belgian did the rest.

Given the quality of the finish, it would be harsh to blame James for the Leicester goal and it should not overshadow what had otherwise been an outstanding performance.

It perhaps underlined how well James had played that when head coach Tuchel made attacking changes with 15 minutes remaining, it was Azpilicueta and not James, despite his error, who was replaced.

But the error provided a reminder that some of these young Chelsea players are still learning on the job and James will no doubt replay the moment many times in his head before Tuchel’s team play Leicester again in the Premier League on Tuesday night.

Tuchel had moved James to deal with the pace and movement of Jamie Vardy, and he did just that as the 34-year-old was largely frustrated.

James used to worship Chelsea striker Didier Drogba and he showed similar strength to the Ivorian in his performance, particularly in the first half.

Vardy clearly fancied his chances of trying to rattle James early on, when he charged towards the academy graduate simply to put the ball out for a goal-kick.

The tackle was a calling card and a warning that Vardy would be swarming all over James, but the England international responded in the best possible fashion.

James played all over the pitch for Chelsea’s academy, so his positional switch at Wembley may not have been as worrying for the player as it was for some of the club’s fans.

But any nerves among supporters over whether or not the youngster would be able to cope were quickly settled. Tuchel led the applause when James muscled Vardy out of the way to let the ball go out for another goal-kick.

And James was in just the right position to get his body in the way of a Vardy shot from inside the penalty area, when the Non-League graduate would have seen a fairy tale unfolding in front of him.

Physically imposing and a wonderful athlete, James is a quiet personality who can come across as shy or even slightly introverted off the pitch.

But there is nothing reserved about the way James plays his football and it was great to hear the Leicester supporters inside Wembley booing when he cleared the ball with a strong challenge on Perez.

England manager Gareth Southgate would have no doubt been interested to see James play in such a big game in a different position.

Southgate loves his players to be able to fulfill a number of roles, but he will also be wary that one misstep of the sort James produced could see England knocked out of the European Championships.

James had produced yet another superb interception ahead of Vardy 10 minutes after half-time, to stop a Tielemans cross reaching the forward, before making the pass that led to Leicester scoring.

Chelsea’s players appealed that Perez must have used a hand to stop the pass from James, but there was no VAR check and the goal stood.

It would have been easy at that point for James to let his head drop or lose concentration, so he deserves great credit for the way he kept going for the final 26 minutes.

But the 89 minutes of excellence will be little consolation for the split-second that was punished, particularly as VAR rescued Leicester at the death. A push on Vardy moments before the full-time whistle only confirmed that.