Your easiest method is actually just letting the opponent lose of last card draw. Just duel a lv10 Legendary duelist and let them run out of cards and you are golden. ^^
Just play vs legendary duelist at lv 10 with a deck using only monsters with higher def and lv4 or less, then in your turn put it in face down def. and wait your oponent attack your monsters, always a lv10 legendary duelist will attack your monsters and he gets battle damage lp, so repeat the process until your oponent get zero lifepoint in his/her turn. This way just took me no more than 5 min.