Lonard, one of four co-leaders after Thursday's first round, shot a 2-under 68 and is through two rounds at minus-7.
Stiles began his second round on the back nine and collected his first birdie at the 13th when he two-putted the par-5 green. He parred his next four holes until the 18th, a hole that could have been a lot worse. Stiles' 5-iron approach from the fairway came up short and right of the green. He chipped through the green, then did it again, but holed his bogey putt from the fringe.
'That putt was probably the key to the round, making bogey there instead of double,' admitted Stiles.
Stiles was not lying about that putt being the key as he caught fire after the turn. He hit an 8-iron 10 feet from the hole to set up birdie at the first, then tapped in a short birdie putt at two. Stiles polished off his third birdie in a row the third when his 8-iron approach stopped inches from the cup.
He made a good par save at the fourth when his drive landed in the right rough. Stiles reached the front of the green, but sank a 7-footer to save the four.
At the par-4 ninth, Stiles hit a sand-wedge to 8 feet. He rolled in the birdie putt to move into sole possession of the lead at the midpoint.
This is the second time this season that Stiles has held at least a share of the 36-hole lead. In Memphis at the FedEx St. Jude Classic, Stiles found himself on top of the leaderboard through two rounds, but ultimately tied for 22nd place.
'I think in Memphis I got ahead of myself and my brain,' acknowledged Stiles. 'Since then, I've realized that you really can't do that, especially out here because all it takes is one or two shots that you're not 100 percent focused on and your round is done.
'I think tomorrow that's my key, is to stay right there in the moment on that specific shot and not get too far ahead.'
Lonard struggled at the par-5 sixth when his 90-yard approach bounced off the downslope and into the gallery.
'Didn't kill anyone,' joked Lonard. 'Everyone was alright. Didn't have to kiss anything better, which was good. That wasn't very enjoyable. I'll blame my caddy on that one.'
He walked off with a bogey, but reclaimed the lost shot at the ninth when his sand-wedge approach stopped 3 feet from the hole.
Lonard split the fairway at the 14th, then hit another wedge to 3 feet. He converted that birdie putt, then punched an 8-iron to 20 feet at the 17th to set up birdie and get within one of the lead.
'I'm driving better than I have all year,' said Lonard. 'I hit a lot of shots that were quality shots and lipped a couple out. I just didn't hole any.'
Brent Geiberger (68), D.J. Trahan (68), Joe Ogilvie (68), Ryan Moore (63), Skip Kendall (67) and Trevor Immelman (65) are knotted in seventh place at minus-5.
The other two co-leaders from Thursday struggled on Friday. Heath Slocum and Harrison Frazar both carded rounds of 1-over-par 71 and are part of a group tied for 13th at 4-under-par 136.
The 36-hole cut came at even-par 140 and among the notable players who will miss the weekend are: 1995 PGA Champion Steve Elkington (141), reigning Rookie of the Year Sean O'Hair (142), defending champion Brad Faxon (145) and FedEx St. Jude Classic winner Jeff Maggert (146).