World number one Rory McIlroy suffered the ignominy of a four-putt triple-bogey as Billy Horschel fired a third-round 63 to surge into the lead at the BMW Championship on Saturday.
While McIlroy's assault threatened to dissolve at the par-three 12th, Horschel vaulted three strokes clear of the field, ending 54 holes at 13-under-par 197 at Cherry Hills Country Club in Colorado.
US Open champion Martin Kaymer (64) and Masters winner Bubba Watson (66) share third place at eight-under 202, five shots adrift of Horschel but still in the hunt.
Ryan Palmer, who was runner-up at the Humana Challenge and The Honda Classic, posted a 67 and is alone in second on 200. Rickie Fowler shot 66 and is in fifth.
But the day belonged to the 27-year-old American Horschel, who is on real form, having shared second place last week at the Deutsche Bank Championship.
Horschel, of Jacksonville Beach, Florida, matched this tournament's 54-hole scoring record with his total of 197. Camilo Villegas set the mark in 2008 at Bellerive golf course and Tiger Woods matched it a year later at the Cog Hill course.
Second-round leader Sergio Garcia, of Spain, stumbled to a two-over 72 and fell into sixth place at 204.
McIlroy didn't fare much better. The Northern Irishman ended up posting a 72, which dropped him into a tie for 10th at four-under 206.
Phil Mickelson, who shared second place in 2012, withdrew before the third-round started, ending his PGA Tour season, and Keegan Bradley also pulled out, citing a rules violation during the first round.
Source: AFP