K.J. Choi of South Korea and Darren Clarke of Northern Ireland tied for the first-round lead at the Sanford International in Sioux Falls, S.D., with matching rounds of 7-under 63 on Friday.
Choi went eagle-birdie-birdie to finish his afternoon, emerging from a pack that includes a four-way tie for third at 6 under.
Choi's bogey-free round included five birdies along with an eagle on the par-5 16th hole. He snuck a 15-foot birdie putt into the cup at No. 18 to hit 7 under.
Clarke later joined Choi, also making a birdie on 18 to reach 7 under. The former Open Championship winner racked up eight birdies and carded just one bogey.
Choi, 51, has yet to win on the Champions Tour and last won a professional event in 2012 at a Korean Tour event. Clarke has two wins on the seniors' tour, most recently the Mitsubishi Electric Championship in Hawaii in January.
Sweden's Robert Karlsson, Australia's Rod Pampling, Matt Gogel and Brandt Jobe sit a stroke back at 6-under 64. South Africa's Retief Goosen, Australia's Mark Hensby, New Zealand's Steven Alker and Mario Tiziani were tied for seventh at 5-under 65.
Defending champion Miguel Angel Jimenez of Spain shot a 4-under 66 to join a eight-way tie for 11th, three shots back.
Steve Stricker turned in a round of 3-under 67, good for a tie for 19th. Stricker is fitting the tournament into his schedule just one week out from captaining the U.S. Ryder Cup team at Whistling Straits in Wisconsin.
Jay Jurecic shot a 3-over 73 in his Champions Tour debut. The American has a spotlight on him this week as he managed to qualify for the Sanford International after resigning from his job as a public school math teacher in Michigan last month in order to pursue his golf dreams.
--Field Level Media