It took Uruguay less than two minutes to open the scoring in the Group B game in Recife when striker Hernandez rose unmarked to head home from a Nicolas Lodeiro corner.
Hernandez sprinted away from a static defence and volleyed past goalkeeper Gilbert Meriel on 24 minutes to add a second and Diego Perez got a third three minutes later when he was left with an open goal after his own header beat the keeper and came back off the post.
Hernandez netted his third and Uruguay's fourth on the stroke of half-time after he beat the offside trap and slotted home from an angle.
Uruguay increased their advantage in the 61st minute when Lodeiro turned Walter Gargano's cross into the net from close range.
Hernandez grabbed Uruguay's sixth from a penalty after 67 minutes and substitute Luis Suarez completed the rout with a seventh and eighth in the 81st and 89th minutes.
"I never imagined this, it was brilliant, but we need to keep it up, the important thing for the team was qualifying for the next stage," the 22-year old Hernandez told reporters.
"I always dreamed of playing and I always wanted to get a chance but I know there are phenomenal players like Suarez and [Diego] Forlan ahead of me. But that's my goal."
Looking ahead to Wednesday's semi-final against Group A winners Brazil in Belo Horizonte, he said Uruguay will not be overawed by facing the hosts.
"They've shown they are a good team, but we also have a good team," he said. "We'll see what happens."
Amateurs Tahiti, champions of Oceania, have been outclassed in the tournament, conceding 24 goals in their three games against Uruguay, Nigeria and world champions Spain.
They used their third goalkeeper on Sunday but although Meriel did not disgrace himself, they never looked like avoiding defeat even against Uruguay's second string side.
The keeper even wrote himself into the tiny island's history books when he saved a penalty from Andres Scotti in the 50th minute.
Scotti's misery was complete a minute later when he got a second yellow card for tripping Steevy Chong Hue but before Tahiti could take advantage Teheivarii Ludivion followed him for an early bath after receiving his second caution on the hour mark.
Hernandez's goal in 79 seconds was the fastest ever at the Confederations Cup and although Tahiti composed themselves and managed to frustrate their more illustrious opponents they never looked like stopping the rout.
"The hard reality is that there is an abyss between professional football and our amateurs," Tahiti manager Eddy Etaeta. "But in spite of the losses and the goals we kept playing fairly and I must thank my players who were wonderful."
The Tahitians were a huge hit with locals and when the final whistle went in Recife their players draped themselves in Brazilian flags and produced a banner for fans declaring: "Obrigado Brasil" (Thank You Brazil).
The official attendance was not revealed but the v
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