The 24-year-old Cappelen, from Denmark, opened with a bogey at the Country Club of Jackson and made eight birdies to take a two-shot lead over Robert Streb, Scott Pinckney and Canada's Nick Taylor.
Cappelen, playing on a sponsor exemption, was an All-American in college at Arkansas. He won the Air Capital Classic in June on the Web.com Tour.
Streb is back in contention two weeks after winning the McGladrey Classic for his first PGA Tour title.
Defending champion Woody Austin had a 70.
Play was suspended because of darkness with 15 players unable to finish.
Keep up with Sanderson Farms Championship second round leaders here.
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