At your level of education and expertise, an entry-level job in a related field -- which is what this is-- should be a no-brainer. Your main challenge will be to convince the employer that you passionately want to be in supply chain purchasing, and that's why you're willing to start at the bottom.
You may find that it's easier for you to get hired at a position slightly above entry level in the supply-chain field, where you won't be quite so over-qualified. Consider getting a professional resume that will highlight your transferrable skills.
Informational interviews are a great tactic to break into a new industry. Call a few department heads at companies that you admire and ask if they will let you do an informational interview. Pepper them with questions about how they would make the transition if they were in your position. Write down everything they say. Often, these are the people who know someone who has a job opening for you, if you impress them.
Best of Luck!