beat (someone) at his or her own game
To defeat or triumph over someone by using his or her own strengths, techniques, or tactics to one's own advantage. He thinks that, because he's so much bigger than me, I won't want to fight with my fists, but I'm so quick that I'll be able to beat him at his own game. The senator keeps saying her policies are the will of the people, but if we can get an accurate poll of her constituency, we can beat her at her own game.