The Briton was fastest in both sessions on the opening day at Yeongam, as Mercedes and Red Bull proved closely-matched in the top four positions.
"I definitely feel like I have a better foundation this weekend," said Hamilton.
"I can't remember the last time I had a pretty strong Friday.
"I'm really happy with the way everything has gone. We have still got some improvements to make but we look like we are competitive."
Hamilton's team-mate Nico Rosberg was third quickest.
Although he was not sure whether Mercedes really did have the edge the times suggested, he agreed his team has a chance of upstaging Red Bull in Korea.
"Red Bull is always going to be very quick but possibly we can challenge," he said.
Mercedes has insisted that its priority for the rest of the season is to finish second in the constructors' championship ahead of Ferrari, which is currently seven points in front.
The Ferraris of Felipe Massa and Fernando Alonso were back in fifth and seventh positions on Friday at Yeongam.
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