hold all the aces
Also, hold all the trumps. Be in a winning position, as in We can't argue with Jeff; he holds all the aces, or If Jean refuses, he'll reveal that he holds all the trumps and force her to give in. These expressions allude to card games in which the ace or a trump card outranks all the others. Also see play one's cards right; trump card.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.