Choi had a bogey-free round at Minnehaha Country Club. The 51-year-old South Korean player won eight times on the PGA Tour.
"Good finish," Choi said. "It's very comfortable here. ... The tournament is going good and the golf course is in beautiful, fantastic shape."
Choi noted the importance of iron shots and putting on a course that is "sometimes confusing in the greens and the slope."
Clarke, the 53-year-old major champion from Northern Ireland, also finished with a birdie on the par-4 18th. He has two victories this season, the TimberTech Championship in November and Mitsubishi Electric Championship in January.
"I just liked this golf course from the first time I came here and I've really, really enjoyed it." said Clarke, who shot 62 on the course last year. "Seems to fit my eye. There's a couple holes where I can open up a little bit and have a dig at it, such as the first today, straight downwind, so I hit driver off the tee and just off the edge of the green and lobbed it up there. I just like the look of the golf course. "
Robert Karlsson, Matt Gogel, Rod Pampling and Brandt Jobe were a stroke back. Mario Tiziani, U.S. Ryder Cup captain Steve Stricker's brother-in-law, was at 65 with Retief Goosen, Steven Alker and Mark Hensby.
Stricker, set to lead the United States against Europe next week at Whistling Straits in Wisconsin, birdied the last two holes for a 67. He won the inaugural event in 2018.
Couples, Furyk and Love will join Stricker at Whistling Straits as assistant captains. Karlsson is an assistant captain for Europe.
Charles Schwab Cup points leader Bernhard Langer shot 70.