My rationale... Bring on Herrera for Matic, Chong for Lukaku. Move Martial central, Rashford left, Chong right. That's an injection of energy and a mix up in attack last 10 minutes would have been enough as the game started to go flat. The advantages... Lukaku taken off for a kid is a kick in the arse and he needs it. It would be a great confidence boost for Chong, but also it might show him his weaknesses, e.g. if he did get bossed off the ball he will know the importance of gym work. Sometimes you need to fail to know what you need to do to succeed. On the flip side he might have had or delivered a Macheda type moment. On the wing he would be lower risk and his pace and skills might have created openings. Also it's a general kick in the arse to all the players to show Mourinho isn't afraid to throw youngsters in the mix if these lot can't give him what is required. As an additional plus the crowd with have got excited for Chong. It might have helped.