I'm from Belgium and I'm traveling by car from Canada to Patagonia (Argentina).
I left the USA just in time (90days) but I got my visa from Mexico 1 day 
after my (90days) VWP expires. 
My plan is to drive to Patagonia and come back to the USA in 6 months. 

Will it be a problem if they see at the US airport that I got my Mexican visa after my US VWP was already expired?

I left within the 90 days. I have an I-94W visa so the date on my passport is the day I have to leave. I crossed the border by car around 7pm but I wasn't able to stop at the border so I drove to Ensenada (because they have an immigration office there as well). But that office was close so I had to wait another day. So that's why my Mexican visa has 1 day difference with my VPW and I'm not sure if that's a big problem if I come back to the us after 6 months. Technically I left the us within the 90 days but will they check when I got my Mexican visa?