Hansen and DeCorso completed 54 holes at 14-under-par 202.
They stand two strokes clear of Henrik Bjornstad (70), Bubba Dickerson (74), Greg Chalmers (68), Neal Lancaster (67), Wade Ormsby (68) and Tom Byrum (67).
Both Hansen and DeCorso got off to flying starts, but it was their steady golf around the turn that put them atop the leaderboard.
Hansen opened with a birdie on the second, then ran off three straight birdies from the fourth to get to 12-under. Hansen parred three in a row from the seventh at The Dominion Club and trailed by two.
DeCorso's start was even better. He followed a birdie on the first with an eagle on the par-5 second. The Canadian kept rolling with birdies on three and four to move to 13-under.
'It was a quick wake-up call that's for sure,' said DeCorso of his fast start. 'It was a part of the golf course that you can take advantage of with two par-5 early. Unfortunately, I had a couple of three-putts, but I'm very, very happy with the round'
As he parred the fifth to 10th, DeCorso found himself tied for the lead as Dickerson, the first- and second-round leader, began to struggle.
Hansen moved to 13-under with a six-foot birdie putt on the 10th. DeCorso responded with a birdie at the 11th to take the outright lead at 14-under.
The lead exchanged hands as Hansen rolled in a five-foot birdie on 12 and DeCorso tripped to bogey on the 13th.
Hansen fell back into a share of the lead at 13-under as he bogeyed the 14th. DeCorso moved one ahead when he birdied the 15th from six feet out.
DeCorso gave that shot right back with a bogey on 16. He bounced back to birdie 17 before parring the last.
'I'm in pain right now. I've taken some medication, but its just not strong enough,' admitted Hansen. 'It is one of those neck problems that hurts with posture and just trying to keep you posture with walking. I'm going to try to get some therapy so I feel better tomorrow.'
After three straight pars, Hansen two-putted for birdie on the par-5 closing hole to join DeCorso in the lead.
'I've been working hard and I worked hard in the off season. I came out a little flat as I was trying to get back into competition mode,' said DeCorso. 'Last week, I hit it terrible. I figured some things out this week and now I'm back to hitting it the way I know I can.'
Chris Riley carded a three-under 69 and was joined in ninth place at 11-under- par 205 by Scott Gutschewski, Greg Owen, Jeff Klauk and Tom Gillis.