I asked Grok (a pretty good AI), by prepending “Verify:” then pasting your question about the order of events. Here’s the first part of the long reply and a link:
The claim is incorrect: Mexico nationalized its oil industry (expropriating foreign-owned assets, primarily from U.S. and British firms like Standard Oil and Royal Dutch Shell) on March 18, 1938, creating the state-owned Petróleos Mexicanos (PEMEX) to manage production.
This predates Iran’s nationalization of the Anglo-Iranian Oil Company (now BP) by 13 years, in March 1951 under Prime Minister Mohammad Mosaddegh.   Mexico’s action was the first major instance of a developing country seizing foreign oil assets, influencing later efforts like Iran’s but facing U.S. and British boycotts that temporarily crippled exports.  
Classic!
Great essay, as usual.
A correction though. The following sentence is incorrect. Mexico was the first country to nationalise Western Oil, decades before Iran.
« The first country to nationalize Western oil, in 1951, was Iran. »
I asked Grok (a pretty good AI), by prepending “Verify:” then pasting your question about the order of events. Here’s the first part of the long reply and a link:
The claim is incorrect: Mexico nationalized its oil industry (expropriating foreign-owned assets, primarily from U.S. and British firms like Standard Oil and Royal Dutch Shell) on March 18, 1938, creating the state-owned Petróleos Mexicanos (PEMEX) to manage production.
This predates Iran’s nationalization of the Anglo-Iranian Oil Company (now BP) by 13 years, in March 1951 under Prime Minister Mohammad Mosaddegh.   Mexico’s action was the first major instance of a developing country seizing foreign oil assets, influencing later efforts like Iran’s but facing U.S. and British boycotts that temporarily crippled exports.  
https://grok.com/share/c2hhcmQtMw%3D%3D_14ec8054-19a1-44a2-a576-36e539594f51
Thanks for verifying my claim. Wikipedia also agrees with me.
Indeed. I barely kept up with who said what, but Mexico seems to be first.