The game engine relies on a random generator. If you do the right things you are likely to win, but fortune also plays a role. That sucks, but we all have to deal with it (suffered under this system in the last days, too. One day 11-0 in the CL away against an inactive player, two days later same formation, same mentality, I won luckily 1-0; today I played 2-2 draw after a last minute goal for a 7 points weaker opponent). That really nerves, but in real football upsets are also possible.