Lucas Glover fired a 9-under 62 on Friday to jump into a share of the lead after 36 holes of the John Deere Classic.
Glover ended 36 holes at 12-under-par 130. Defending champion Zach Johnson managed a 5-under 66 to end alongside Glover.
The two former major champions share the lead with Patrick Reed, who fired an 8-under 63 on Friday.
Matt Jones posted a 65 and is alone in fourth place at minus-11.
Jerry Kelly and Troy Matteson both fired 64s to jump to 10-under 132. They were joined in fifth place by David Hearn (66), Kevin Streelman (66) and Daniel Summerhays (67).
Three-time champion Steve Stricker (66) is one of five players tied for 10th at minus-9.
Camilo Villegas, who shared the first-round lead with Johnson at TPC Deere Run, struggled to a 2-over 73 and he tumbled into a tie for 36th.
Glover, the 2009 U.S. Open champion, rolled in a 7-footer birdie on his first hole, the 10th, then stuffed his approach inside a foot at the 12th. After kicking that in, he parred the next three.
The 33-year-old converted back-to-back birdies at 16 and 17, to make the turn at 7-under. He birdied the first two holes around the turn to get within three of Reed, who was already finished.
Glover birdied the fourth from just inside seven feet, then birdied the sixth and seventh from about five feet out to join Reed atop the leaderboard. Glover parred his final two holes to be the last in at minus-12.
"I've been struggling. I was ecstatic to shoot 3-under yesterday. You can imagine how I feel today," said Glover, who broke par in back-to-back rounds for the first time since the first two rounds of the Wells Fargo Championship in May.
Johnson got up and down for birdie at the par-5 second and later holed a birdie try from off the green at the eighth to head to the back nine at minus-10.
The 2007 Masters champion drained a 13-footer for birdie at 12 and an 18-foot try at 14 for another birdie. Johnson grabbed a share of the lead when he got up and down for birdie at the par-5 17th.
"Today was a hard 66. Yesterday was a much easier 64," Johnson admitted. "I didn't drive it very well, but the positive side is I know I can play here if I don't drive it. My short game was tremendous. I putted great and I chipped it even better."
Reed, who is winless as a professional, was in the first group out off the 10th tee Friday. He started with birdies at 11 and 13 before a poor drive at the 14th cost him a stroke.
The 22-year-old PGA Tour rookie bounced back with a 16-foot birdie putt at the 16th. Reed followed that with a chip-in eagle at the 17, which helped him make the turn at minus-8.
Reed had back-to-back birdies from the second, and again from the fifth. He parred the last three holes to be the first one in at minus-12.
"It's definitely a team. I mean, she helps me with everything. I never check the wind. She tells me what the wind is," said Reed of Justine, his caddie and wife. "She helps me pick most of my clubs. She seems to know my distances better than I do. She's great at reading putts. So I kind of have the full package."
NOTES: Johnson posted his 18th straight round in the 60s at this event ... Darron Stiles had a hole-in-one on the par-3 seventh and that helped him make the cut on the number of minus-4 ... Seventy-two players made the cut, but Robert Allenby, Ben Kohles, Ben Crane, Robert Karlsson, former British Open champ Louis Oosthuizen and Sean O'Hair were among those that missed the cut ... Jeff Overton withdrew during the second round with a wrist injury.