All of the “Win X Competition or Cup” achievements can be simulated to save time and effort.
Simply go to start the competition and select the best 8 teams in that competition to be controlled by yourself, and then simply simulate to the end of the competition or cup. To Simulate a match instead of playing go down to simulate and press or in some competitions you can go to fixtures and then find the last one and simulate to this, also to save time if your squad line up needs to be changed then you can press and this will be done for you.
99% of the time one of you 8 teams will win the competition and the achievement will unlock just make sure that after the group stages at least some of your 8 teams have not lost or drawn any games.
Obviously if you want to you can play and win the tournament by finishing each match.
The best 8 teams in this competition are:
Australia, England, France, Ireland, New Zealand, Scotland, South Africa and Wales.