Three birdies in his last four holes gave John Cook a two-shot lead after the second round of the Western Open in Illinois.

The 44-year-old American finished with a six-under-par 66 to go to 11 under for the tournament.

He is two clear of fellow countryman Jonathan Byrd, Fiji's Vijay Singh and Stuart Appleby of Australia.

Among those one shot further adrift are Bob Estes, who won the tournament in 1985 as an amateur, Scott Verplank and Australia's Robert Allenby.

Cook had a bogey-free round and recorded three birdies on each nine. He has not dropped a stroke since his opening hole on Thursday.

"I hit the ball very solidly but I had to make a couple of putts early to keep the round steady," said Cook.

"Once I did that, and I started to feel pretty comfortable from the fifth onwards. I really played very well, didn't miss a shot, and made a couple of good putts."

Cook missed the cut at the recent US Open and has spent some time since then away from the tour playing a few holes with his son Jason, who was preparing for a couple of amateur tournaments.

Cook's game took off after a birdie at the par-five 15th, where he hit a driver and three-wood close to the green, pitched to eight feet and made the putt.

Serious

After a birdie at the 16th and a par at the next, Cook hit a six-iron approach to four feet at the 18th and sank his birdie putt.

Appleby, who has not won on the tour since the 1999 Houston Open, reeled off six consecutive birdies at the start of his round to set him up.

It matters how you drive and putt together because if you want to be serious about shooting a good score you want to give yourself opportunities," he admitted.

Britain's Luke Donald is six shots behind Cook after a second-round 70.

Second round scores from the Advil Western Open (USA unless stated):

133: John Cook 67 66
135: Jonathan Byrd 67 68, Vijay Singh (Fij) 68 67, Stuart Appleby (Aus) 70 65
136: Scott Verplank 67 69, Robert Allenby (Aus) 69 67, Joe Durant 68 68, Bob Estes 66 70, Jerry Kelly 67 69, Neal Lancaster 68 68
137: Paul Gow (Aus) 69 68, Davis Love III 67 70, Rocco Mediate 69 68
138: Luke Donald (Gbr) 68 70, David Gossett 65 73, Brandt Jobe 69 69, Steve Elkington (Aus) 71 67, Franklin Langham 68 70
139: Stephen Gangluff 69 70, Cameron Beckman 73 66, Harrison Frazar 71 68, Joey Sindelar 69 70, Tom Byrum 68 71, Lee Janzen 72 67, Shaun Micheel 69 70, Carl Paulson 71 68
140: Matt Gogel 70 70, JJ Henry 70 70, Briny Baird 71 69, Chris Riley 70 70, Kevin Sutherland 75 65, Duffy Waldorf 70 70, Joel Edwards 69 71, David Frost (Rsa) 67 73
141: Ben Crane 71 70, John Senden (Aus) 71 70, Jess Daley 74 67, Tim Clark 70 71, John Rollins 73 68, Craig Barlow 70 71, Rory Sabbatini (Rsa) 71 70, Jeff Sluman 70 71, Steve Stricker 74 67, David Toms 68 73, Glen Day 69 72, Brent Geiberger 73 68, Jonathan Kaye 71 70, Justin Leonard 69 72, Steve Lowery 70 71, Blaine McCallister 69 72, Scott McCarron 69 72, Frank Nobilo (Nzl) 71 70, Tom Pernice Jr 69 72, Nick Price (Zim) 73 68.