The 29-year-old enjoyed seven birdies as he moved to 15 under par despite his bogey on the par-four sixth hole.
After his second-round outing, Poston told pgatour.com: "I feel great. My last few rounds out here have been great going back into last week, so just going to try and keep riding that momentum and doing what I'm doing."
The American arrived at Silvis, Illinois, on the back of a second-place finish at last week's Travelers Championship. He added: "Last week, the one thing I think I learned after playing well Thursday was to try and keep the pedal down.
"I think this golf course may yield a few more birdies than last week but at the same time, you got to go out there and hit some golf shots to stay aggressive. I was able to do that, which is nice."
Poston's six-under-par performance on Friday was matched by fellow American Denny McCarthy, who currently sits second on the leaderboard with 11 under par.
Argentina's Emiliano Grillo joined the 10 under club as he shot 64 in the second round. He was later joined by Austria's Mathias Schwab and Americans Christopher Gotterup and Chris Naegel.
The lowest rounds on Friday were a pair of seven-under-par 63s, scored by Maverick McNealy and Kelly Kraft. Both players are in an eight-strong group at nine-under - a group which also includes England's Callum Tarren.
Meanwhile, the defending John Deere Classic champion Lucas Glover missed the cut by one shot despite a second-round score of 66. The American bowed out of the event on two under par.