The Mexican handed his Argentine opponent his first professional defeat at the Hard Rock Hotel & Casino, with the cards reading 117-110 (twice) and 116-111 in his favour.
Southpaw Sanchez had appeared within the limits at the weigh-in. He was one pound over the 115lb limit at Friday's second weigh-in but thought he had two hours to make weight under IBF rules.
However unbeknown to Sanchez and IBF supervisor Aaron Kizer, the US state of Nevada has different rules, with fighters only given one hour to make weight.
So when Sanchez returned in what he thought was good time, local boxing authorities had already declared him overweight, despite Kizer announcing he had made weight.
Sanchez had won the belt off Rodrigo Guerrero in February 2012 and successfully defended it against Juan Alberto Rosas and Rodel Mayo.
Even if this fight was not to be a third title defence - his victory means the belt remains vacant, whereas Sosa could have won it with victory - it was to provide a degree of consolation to him.
Sanchez, 22, impressed in rocking his 28-year-old opponent in the fourth round and putting him on the canvas 30 seconds from the end. He improves to 16-1-1 (8 KOs).
The tough Sosa kept coming forward, but fell short and is now 24-1-0 (14 KOs).
- Sports & Recreation