The phrase "ace card" generally means having a secret weapon or advantage that can help you win or achieve success in a particular situation. Full definition
Unless it's got some amazing ace card up its sleeve, Drawn to Death is definitely a game you'll want to avoid. (stevivor.com)
Practicality is clearly the VW's ace card with a 10th place, while economy, safety, infotainment and comfort received good scores. (autoexpress.co.uk)
Your ace card will be that you'll set up and conduct your business professionally, perhaps offering add - on services such as space for temporary, in - between moves storage. (entrepreneur.com)