Chalmers completed 36 holes at 8-under-par 132, where he was joined by Brad Fritsch (65) and D.A. Points (64).
David Branshaw (66) and Dustin Bray (67) are one stroke back at minus-7 as there are 15 players within three strokes of the leaders.
Chalmers, who was in the second group out off the first tee, moved in front with three birdies between the fourth and eighth holes. Those birdies moved Chalmers to 10-under.
The 34-year-old stumbled to a double-bogey on the par-4 10th. He recovered those strokes with birdies at 11 and 12 at Elmhurst Country Club.
Chalmers faltered to another double-bogey on the par-3 13th. He moved to minus-9 thanks to a birdie at 14, but Chalmers gave that shot back as he bogeyed the 16th.
'I played really nicely the first nine holes and then quite average for a couple holes on the back nine,' Chalmers said. 'I made some bad decisions and it cost me dearly. I think I was probably fortunate to come away with only two-over on the back nine after two doubles and a bogey.'
Points carded three birdies on the back nine, his opening nine, to move to minus-five. After a birdie on the third, he tripped to a bogey at the par-3 fifth.
The 2004 champion at this event, Points bounced back with an eagle on the par- five sixth. He birdied the eight to grab a share of the lead.
'I made about a 20-25 footer on No. 10 and I thought, 'Oh wow, I haven't made too many of those in a while,' Points stated. 'It was a nice way to start.'
Fritsch opened with a bogey on 10, but recovered with a birdie on 11. He moved into the lead with six birdies in an 11-hole span. However, he faltered to a bogey at the ninth, his last, to fall into a share of the lead after two rounds.
'It's just nice to be on the right side of the cut. I've missed four in a row,' Fritsch said. 'I drove it fairly well and wedged it within tap-in distance a couple times and I played both par-fives very well.'
Cameron Percy, Rick Price, Scott Piercy, Jeff Curl, Won Joon Lee and Chris Kirk are tied for sixth at 6-under-par 134.
The cut line fell at 1-under-par 139 with 65 players making the cut. Among those missing the cut were the Nationwide Tour's leading-money winner Jarrod Lyle (140) as well as No. 5 on the money list Colt Knost (143) and No. 6 on the money list Darron Stiles (143).