http://consulmex.sre.gob.mx/nuevayork/index.php/en/component/content/article/182-informacion-general
Other nationalities, Non-US Permanent Residents. Starting May 1st, 2010, all those foreigners, regardless of their nationality, visiting Mexico for tourist, business or transit matters won't need a Mexican visa as long as they have with them a valid and not expired USA visa in the passport. In this context, if you have a valid US visa in the passport you do not need to obtain a Mexican visa