The striker missed much of the offseason and early season with injury, but is now off the mark for United in the new campaign.
Just after halftime, the Mexican international striker made a clever run to lose his marker at the 6-yard box and volleyed home Wayne Rooney's corner acrobatically with the inside of his right boot.
The goal was enough to lead United to a win against rival Liverpool at Old Trafford, and sent the Red Devils into the fourth round of the Capital One Cup.
Hernandez was making his first start of the season for United. He previously made two substitute appearances in the Premier League, and one against Bayer Leverkusen in the Champions League.
The news will come as a boost for Mexico's national team, which needs Hernandez to be sharp ahead of two crucial World Cup qualifiers against Panama and Costa Rica next month.