The Hamilton golfer Steven Alker is just four shots off the pace after 36 holes of the latest PGA tournament in Illinois.
At eight under for the tournament in a tie for 11th, Alker trails the American Justin Thomas who leads by one stroke.
Alker's two under par second round 69 featured a bogie and three birdies after his 1st round 65 lifted him into the top 10 in a tie for 6th.
Rotorua's Danny Lee, who notched his maiden PGA tour victory last week, trails Alker by two strokes.
Back to back rounds of 68 has propelled Lee into a tie for 22nd after his blemish free second round that featured three birdies on the front nine.
World number two Jordan Spieth shook off the rust that cost him in the opening round as he fired a sparkling seven-under-par 64 to surge into contention.
The Masters and U.S. Open champion, playing his first PGA Tour event in three weeks, mixed an eagle at the par-five second with six birdies and a lone bogey to finish the second round at seven-under 135, five strokes off the pace.
Long-hitting Justin Thomas, co-leader overnight, fired a five-birdie 67 at the TPC Deere Run to take over on his own at the top, with fellow Americans Johnson Wagner (63) and Tom Gillis (65) a further stroke back at 11 under.
Spieth, who took time off after his U.S. Open win at Chambers Bay last month, was delighted to rebound from an opening 71 where his short game was especially rusty.
"Today was a big step forward," said the 21-year-old, who is using the tournament to tune up for next week's British Open where he will aim to add the third leg of a grand slam of the majors.
Some have questioned the plan by Spieth to arrive at St. Andrews just three days before the start of the British Open but the American is happy with his preparations for the year's third major.
"I got a good amount of practice in and I'll be able to adjust to the speed and the conditions there," he said. "I feel like I'll be able to do that in a couple days.
"It is a career goal of mine to have a career grand slam (of the majors). If it happens in one year, that would be pretty special. I'm just focused on St. Andrews."
Rookie Thomas, seeking his first PGA Tour victory, was "very excited" to be leading after 36 holes.
"I stayed really patient, I kept hitting my lines and my birdies were pretty low-stress," said Thomas. "I'm in a good spot."
The cut fell at four-under 138 with former major winners Lucas Glover, Retief Goosen, Trevor Immelman and David Toms among those in failing to advance.