Following his nine-under 62 on Thursday, the 35-year-old Dane carded a 66 in the second round, highlighted by a birdie on his final hole - the par-4 ninth - after a precise recovery from the rough.
Olesen also bounced back from a double bogey on the par-4 15th with back-to-back birdies to finish at 14-under 128.
"I think both days, my iron play has been really, really good," said Olesen, who is still chasing his first PGA Tour win. "I hit a lot of shots really close to the pin and gave myself a lot of good chances. Today, there was like two or three bad drives that costed me, but I still felt pretty good over the ball."
Knapp stayed bogey-free through 36 holes for the first time in his career, shooting a 65 to sit one stroke back. The 2024 Mexico Open champion began his round with birdies on Nos. 10-12 and is looking for his second PGA Tour title of the season.
"I feel like it's been... kind of mistake-free for the most part," Knapp said. "I haven't really had to scramble too much."
Pierceson Coody (65) is two shots behind Olesen, tied with Sam Stevens (68), who bogeyed his final hole. Takumi Kanaya (64), Chris Kirk (67), and Matti Schmid (68) are all at 11 under.
With just two weeks left in the regular season, players like Knapp (55th), Schmid (68th), and Kirk (77th) are battling to stay inside the top 70 in the FedEx Cup standings and qualify for the playoffs.
Meanwhile, Adam Svensson, who fired a course-record 60 on Thursday, tumbled down the leaderboard with a second-round 75. Notable missed cuts included Byeong Hun An (67th in FedEx Cup) and Haotong Li, who tied for fourth in the British Open.
Kurt Kitayama came out firing at the 3M Open on Sunday, birdieing six of his first eight holes before holding his nerve down the stretch to secure his second career PGA Tour title.
Thorbjorn Olesen and Akshay Bhatia will take a one-shot lead ahead of four players as the 3M Open heads into the final round on Sunday.
Canada's Adam Svensson fired the lowest round in the seven-year history of the 3M Open to open up a two-shot lead after Thursday's opening round in Minnesota.
An incredible final round 61 was enough to see William Mouw grab his maiden PGA Tour title at the ISCO Championship in Kentucky on Sunday.
