Attorney General Jesus Murillo Karam confirmed that Alexander Mora, 19, was identified among charred remains found in a landfill and a nearby river, bolstering suspicions that all 43 young men were slaughtered by a police-backed gang in September.
Authorities had sent 17 badly burned remains to an Austrian medical university last month after the Guerreros Unidos cartel confessed to executing the students in the southern state of Guerrero.
Murillo Karam said more tests will be conducted on the remains sent to Austria that have still not been identified.
If all the students are confirmed dead, it would rank among the worst mass murders in a drug war that has killed more than 80,000 people and left 22,000 others missing since 2006 in Mexico.
The case has sparked nationwide protests, highlighted Mexico's struggle with corruption and undermined President Enrique Pena Nieto's assurances that his security policy was bearing fruit.