#1. Losing possession in key areas
Although Jose Mourinho's team does not play a possession-based game like his predecessor and focuses mainly on hitting teams on the counter, keeping the ball against a side like Chelsea is essential.
No team can afford to let the likes of Hazard, Morata and the magnificent midfield that Chelsea have, dominate the ball, even if that team may have arguably the best defence in the league.
Mourinho's men were very wasteful and impatient in possession and gave the ball away 19 times in the final third and once even in their own box. United tried to play a whopping 79 long balls in an attempt to escape from the hole Chelsea dug them in.
A major yet latent factor in United's inability to keep possession was the return of Chelsea's backroom hero, N'Golo Kanté. As usual, Kanté was all over the pitch covering every blade of grass and eliminating passing options for the United man on the ball.
United failed to counter the 2-time Premier League winner and had to surrender possession and put their backs to the wall in order to absorb all the Chelsea pressure.