Vela converted from the penalty spot in the 26th minute after Jang Hyun-soo handled the ball while trying to stop a cross from Andres Guardado.
Hernandez would not be denied again, though, the West Ham striker making no mistake in drilling in his landmark goal to send the raucous Mexican crowd into raptures.
Despite their overall boisterousness, Mexico's fans didn't use their usual controversial "eh, puto!" chant during goal kicks taken by the South Korean goalkeeper.
Led by Tottenham's Son Heung-min, South Korea can't be overlooked by a Mexico side that has big goals following its statement victory.
With a 2-0 lead in the second half, El Tri faithful took to chanting "Profe Osorio" in support of the team's Colombian coach Juan Carlos Osorio, who before the tournament had been heavily criticized by pundits and a football-loving public for his tactics and management of the national team.
Mexico had their second of the game in the 66th minute, however, when Hernandez collected a super pass from Lozano before finishing low into the bottom corner of the net to register his 50th global goal.
The closest they came to scoring in the first half was with a header from a corner which Mexico goalkeeper Guillermo Ochoa tipped over the bar.
Miguel Layun pressed for a second goal before the break but his shot from a low cross-field drive was tipped away by Jo Hyeon-woo.
The record for penalties at the World Cup stands at 18 in 2002.
Hernandez also scored for Mexico on June 23 at the last World Cup, netting in a 3-1 defeat of Croatia. As if anyone didn't know it, Son is the team's best player by a distance.
Mexico so far is one of the teams that has a flawless run in the campaign and has conceded just one goa.
"We didn't listen to the criticism", said Javier Hernandez, one of the scorers against South Korea.
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