Scott Sterling, Shane Bertsch, Paul Gow and Wook-Soon Kang share third place at 5-under-par 67. Anthony Painter, Jason Schultz, Kyle Thompson, Ben Bates and Kevin Johnson are one stroke further back at minus-4.
The 39-year-old Boros started on the back nine at Fox Den Country Club and opened with a birdie on the 10th. However, he stumbled to a bogey two holes later to slide back to even par.
Boros then parred four straight holes. From there, he caught fire. Boros dropped in back-to-back birdies from the 17th. Around the turn, he moved to 3 under with a birdie at the third.
Boros, a three-time winner on the Nationwide Tour, drained consecutive birdies from the sixth and grabbed a share of the lead with a birdie at the ninth, his last.
'I played well and putted well,' said Boros, who held the lead after the first round of the Chitimacha Louisiana Open earlier this year. 'My game has been coming around. It was a good combination today. It is easy to say the course sets up well for you when you are playing well. But I do feel comfortable on this course.'
Olsen, like Boros teed off in the afternoon group, got off to a hot start. He eagled the par-5 first and came right back to birdie the second. Olsen moved to 4 under with a birdie at the par-5 fifth.
Olsen, whose best tour finish was a tie for 17th at the 2000 Permian Basin Open, birdied the eighth to get to minus-5 before rolling off five consecutive pars.
The 37-year-old picked up his fourth birdie of the day at the par-3 14th. Olsen, who has made four of 14 cuts on the PGA Tour this season, then moved to minus-7 with a birdie at the 17th, but faltered to a bogey at the last to share first place with Boros.
'I wish I was at the Memorial, but I'm not and I'm glad to be here,' said Olsen. 'This is a great tournament. I'm happy with my start. I'm playing good enough to win. But if you're going to be low after four, you've got to be low after one round.'
Two-time winner on tour this season Jimmy Walker stands at 3-under-par 69 where he is joined by a large group of players that includes Jacob's Creek Open Championship winner Euan Walters and last week's SAS Carolina Classic champion Chris Anderson.
Ty Tryon, Johnson Wagner, Zoran Zorkic and Keoke Cotner pace a group of 21 players at 2-under-par 70.