"The greens were trickier than I expected, but my putter came through and helped me put together a good round," he said.
In the opening round, playing partner Brooks Koepka posted an 8-under 63 to sit one stroke off the lead.
Defending champion Scottie Scheffler signed for a 5-under 66 to stay within striking distance of back-to-back titles.
American Taylor Moore held the sole first-round lead at 9-under par following a flawless, bogey-free performance featuring nine birdies.
Moore is chasing his second career PGA Tour victory, three years after winning the 2023 Valspar Championship.
Other South Korean players remained in the field after the opening round.
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Noh Seung-yul was tied for 32nd place at 4-under, while Im Sung-jae and Kim Joo-hyung both shot 3-under par to share 47th place.
