@webebucks. Leaving for CUN in four weeks. Passports expire in September. Similar situation as yours. How did you fare? What happened?
@Michael F. Hey Michael. You'll be completely fine. There is alot of bad info out there because there used to be a rule that the passport had to be valid 6 months out. I actually called the State Department before my trip to confirm that this is no longer the case. A passport only has to be valid through the time that you return from Mexico.
Getting out of the US may be the issue...the airlines...at-least in the US. Best hope that the information you phoned about has filtered down to every gate attendant, etc. Note airline tickets are your current planned return based on your airline tickets in hand. But shit happens and plans change. Also the travel/tourism allows you to stay for up to 6 months. Hence it is best that current passport covers this period of time. Thanks for the info. I will check it out and see if I can find something in writing.
Another site has opinion that this should not pose a problem: Do U.S. Citizens Need a Passport to Travel to Mexico?