Son's fantastic 92nd minute strike was the only bright spot for the Koreans in a match which was dominated by Mexico.
Carlos Vela (26th minute) and Javier Hernandez (66th) had earlier handed Mexico a 2-0 lead.
With two back to back losses, South Korea's hopes of reaching the knockout stages will depend on the results of the other matches in their group, reported Yonhap news agency.
On the side, having earlier stunned defending champions Germany, Mexico are sitting pretty atop Group F with six points.
For the second straight match, South Korea allowed a goal on penalty. In the 24th minute, defender Jang Hyun-soo was called for a handball violation when he blocked an Andres Guardado cross with his right arm while sliding in the box.
Two minutes later, Vela struck it past keeper Jo Hyeon-woo with his left foot for a lead that Mexico would never relinquish.
Hernandez, also known as 'Chicharito', netted his 50th career goal for Mexico in the 66th, with Hirving Lozano setting him up on a breakaway.
It was Lozano returning the favor to his teammate, after Hernandez assisted on Lozano's goal against Germany in a similar play.
Son saved South Korea from the brink of another clean sheet loss, but it was too little, too late for his side.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
