Cameron Beckman posted a 3-under 68 and is tied for second place with Jason Dufner, who shot a 2-under 69 on Saturday. The pair is knotted at minus-4.
Allan wasted little time in getting into red figures on Saturday. He reached the par-5 first green in two with a rescue club, then two-putted for birdie from 40 feet.
He parred his next three holes, then collected his next birdie at the next par five. Allan laid up with his second shot at the fifth, then played a wedge to 15 feet to set up birdie. He made it two in a row with an 8-footer at the sixth.
Allan parred out on the front side, but flew up the leaderboard thanks to his play at the start of the second nine. He rolled in a 15-foot birdie putt at 10, then hit a 6-iron inside 3 feet for the easy birdie at the par-3 11th.
Allan collected his third birdie in a row at the 421-yard, par-4 12th. He knocked his 9-iron approach to a foot and kicked in the short birdie putt.
That would be Allan's last birdie as he parred his remaining six holes for the 54-hole lead.
'Luckily today I hit most of the fairways so that gave me an opportunity to hit some good irons,' said Allan. 'I've struggled with my putting this year, but I'm rolling it good this week.'
If Allan can advance to the winner's circle Sunday afternoon, it would be his first on the Nationwide Tour. He played the PGA TOUR the last five years and earned two runner-up finishes.
It doesn't hurt that the LaSalle Bank Open features the largest purse on the 2006 Nationwide Tour schedule.
'Obviously this tournament has the biggest purse of the season, but the less I think about winning it, the better chance I have,' admitted Allan. 'I was looking forward to coming here.'
Second-round co-leader Richard Johnson only managed a 1-over 72 on Saturday. He is tied for fourth place with Cliff Kresge, who carded a 3-under 68, at 3-under-par 210.
Nicholas Thompson, who shared the 36-hole lead with Johnson, was two worse than his fellow co-leader. He shot a 3-over 74 and is knotted in sixth place with Matt Hendrix, who posted a 3-under 68. The pair is tied at minus-1.
Bob Heintz (67), Chris Baryla (71), Doug LaBelle II (72) and Steve LeBrun (72) share eighth place at even-par 213.