Kobbie Mainoo had played as a No.10 before - but in a game at Leigh Sports Village. That's where most Manchester United academy games are held and fixtures are attended by a couple hundred supporters, so playing in that role at the National Arena in Bucharest was a different kettle of fish.
The National Arena, the biggest stadium in Romania, had been sold out for months in anticipation of United's visit in the Europa League, but Mainoo starred in an FA Cup final and the final of the European Championship last year, so he was never going to be fazed by the occasion.
Ruben Amorim started Mainoo as the left-hand side No.10 against FCSB, despite the general assumption being that he would play in the pivot when the starting teams were confirmed.
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Toby Collyer started alongside Bruno Fernandes in the pivot, and Christian Eriksen lined up in the right-hand side No.10 position. Amorim started Fernandes in a deeper role for a third successive game and he recently explained it was a switch made in an attempt to "have more of the ball".
The change has had the desired effect, as United had 68 per cent possession against Rangers and 69 per cent of the ball in the first half against FCSB, although chances were at a premium for both sides in the opening 45 minutes in Bucharest and the best opportunity fell to Mainoo.
Rasmus Hojlund did brilliantly to pull the ball back to Mainoo, but the youngster fired his shot over the bar and Eriksen reacted by putting his hands over his head. Mainoo should have scored, but it was interesting that he got into that position, a direct result of him playing in a new role for the first team.
Although Mainoo was predominantly used as a hybrid No.6/No.8 by Erik ten Hag, Amorim pushed him further up the pitch against FCSB and the youngster looked very comfortable.
He looked to enjoy having a new-found freedom on the left side of the pitch and he combined well with those around him, which almost led to a goal when Lisandro Martinez stepped out and played a beautiful pass over the top to Mainoo, who took it down but couldn't produce the finish.
Mainoo has been described as "press-resistant" by those who know him best and his ability to excel in tight spaces makes him a good fit for one of the No.10 roles in Amorim's formation.
Earlier this month, Amorim warned Mainoo still has a long way to go in his development and there have been some lingering doubts about whether he fits into the new boss' plans, but Mainoo made a step forward against FCSB and demonstrated his quality in a new role.
Amorim made changes at half-time, introducing Amad and Alejandro Garnacho to the game, and he had the option of dropping Mainoo back into the midfield pivot. However, Amorim kept Mainoo in the No.10 role and that was a compliment to the 19-year-old's first half performance.
Mainoo did slightly change his role, as he switched to the right-hand side No.10 role, but that didn't disrupt his rhythm, and he provided an excellent assist for Diogo Dalot's opening goal.
The youngster then added the icing on the cake to his performance when he made it 2-0, calmly slotting home from inside the box to make amends for his missed chance in the first half.
Until Thursday night, Mainoo hadn't really been considered as an option for one of the No.10 roles, although that should change for the remainder of the season after his polished display.
Mainoo is an exceptional talent and is too good to start most games on the bench. The onus was on Amorim to find out which position suited Mainoo best in his system, and it felt like he found the answer in Bucharest.
