Hearn had 10 birdies and one bogey and fell two strokes shy of the course record at Cliffs Valley, one of three host courses this week. His 63 was also the lowest opening score in tournament history.
'I was playing the more scoreable of the three courses so I wanted to get off to a good start,' said Hearn. 'I did that and more today.'
The top five players on the leaderboard all played Cliffs Valley on Thursday.
Todd Dempsey and Tommy Gainey both shot 7-under 65 and were two shots off the lead in a tie for second place. Erik Compton and James Driscoll were another shot further back at 66.
Jimmy Walker and Jim McGovern shot 66 at Keowee Vineyards and shared sixth place with Richard Johnson, who had a 66 at the third course, Walnut Cove.
In addition to the Nationwide Tour professionals playing this week, there are also a host of celebrities competing in the Pro-Am, including actors Kevin Costner and Greg Kinnear; and professional athletes John Elway, Wayne Gretzky, Brett Hull, Jim Rice and Sterling Sharpe.
Gary Player, the 71-year-old Hall of Famer from South Africa, is also playing for the fourth year in a row. He opened with an 11-over 82 at Walnut Cove and was one shot out of last place in a field of 168.
Among the serious challengers, Hearn was the story.
Hearn hit 13 of 14 fairways and 14 greens in regulation to spark two significant birdie streaks in his round. He made three consecutive birdies from No. 4, then four straight from No. 11 to highlight his lowest-ever score.
He's had rounds of 64 twice on the PGA TOUR, and once on the Nationwide Tour.
'It is difficult to say it is my best round because it's only Thursday, but it is definitely my best score,' Hearn said. 'I didn't really hit any remarkable shots, but I didn't really hit any poor shots either. It was just a solid round.'
Cliffs Valley will host the final round Sunday.