Daniel Summerhays, who is seeking his first PGA Tour win, fired a nine-under-par 62 on Saturday to grab a two-shot lead after the third round of the John Deere Classic.
Canada's David Hearn shot 64 and moved into second place at 17-under, while defending champion Zach Johnson, of the US, dropped into third at minus-16 as the field heads into Sunday's final round.
The 29-year-old Summerhays shot a career low round Saturday and is 19-under 194 through 54 holes at TPC Deere Run. American Summerhays missed three consecutive cuts before tying for ninth at last week's Greenbrier Classic.
Summerhays rolled in 10 birdies while matching the lowest third-round score in event history.
"I think when I'm playing well the mentality is make as many birdies as you can," Summerhays said. "I'm really looking forward to (Sunday). I'm playing really well."
J.J. Henry (65) and Jerry Kelly (66) are tied for fourth at 15-under, one shot in front of Nicholas Thompson (64), Chris Kirk (66) and Matt Jones (68).
Summerhays has been on a hot streak all week at the Deere Run course.
"I know there's going to be obstacles and challenges, as there always are. There are always things that stand in your way. But I'm just excited to see what those are and deal with them," Summerhays said.
Hearn closed with three birdies in four holes to get within two strokes of Summerhays.
Johnson drained a 60-foot putt for an eagle on No. 2 but made bogey on the par-four No. 6 and the par-four 11th hole.
Johnson says he is confident heading into the fourth round.
"I certainly think there were a lot more positives out there than negatives," Johnson said. "My putter has been great. Even the ones I've missed have been great."
American Steve Stricker is eight shots behind Summerhays after shooting a 69 Saturday.
Stricker is trying to claim his fourth title at this event in the past five years.
"I'll just have to come out and do the best that I can, and like I say, put up a low number," said the three-time tournament winner Stricker. "And they're out here. The low number is out here."