How can I lose this match

20 V 17.6 is not alot of exra quality really!, and that is taken over your whole squad!, you may have played your best team with your best formation, tactics and orders but that does not mean that you will win or that they are correct!, your opponenet knowing you had a stronger team will have either set his orders to hard tackling to try and controll the posession and tackles!, he will have set to attack to go at you!, you have not shown us a screen shot of you and your opponenets formation 7 tactics plus your live match stats!, this wil give us an indecation of how the game panned out!.
There are many many other variables which effect the outcome of games such as morale, condition, his player quality in key areas!, age of the team, playing in the correct position , orders, arrows etc so dont get to annoyed for one loss just look at how to stop it happening again.