Lake Forest - Red-hot Jason Day extended his lead and continued to dominate the golf world as he stormed five shots clear after the second round of the BMW Championship at Conway Farms Golf Club on Friday.
The Australian world number three backed up his opening 61 with an eight-under 63, including a 43-foot eagle putt at the last, to rocket to 18-under 124 in the third of the PGA Tour's four FedExCup playoff events.
Day tied the PGA Tour record low for the opening 36 holes as he built a commanding five-stroke advantage over Americans Brendon Todd and rookie Daniel Berger.
Todd holed out from the fairway for an eagle at the par-five 18th for a 63 of his own while Berger fired a 64 to post a 13-under total of 129.
World number two Jordan Spieth, who played with Day for the first two rounds, was a further two shots back after finishing birdie-eagle for a 66, level with fellow American Kevin Na (66).
Earlier, Day fell short in his bid for a record-equalling 59 in the weather-delayed opening round when he failed to hole out a 44-yard chip shot from the right rough, then missed a nine-foot birdie putt.
But the disappointment did not last long as he went back out and once again destroyed the Conway Farms course with seven birdies, an eagle and just one bogey.
Day is now a mind-boggling 97 under par for his last 26 PGA Tour rounds.
The Australian is searching for a fourth win in six starts and world ranking officials have confirmed he will rise to number one for the first time if he wins this week's tournament.
Current world number one Rory McIlroy was nine shots off the pace after 36 holes in a tie for ninth after carding a 65.
Leading second-round scores on Friday in the $8.25 million BMW Championship (USA unless noted, par-71):
124 - Jason Day (AUS) 61-63
129 - Daniel Berger 65-64, Brendon Todd 66-63
131 - Kevin Na 65-66, Jordan Spieth 65-66
132 - Justin Thomas 65-67, George McNeill 67-65, Scott Piercy 67-65
133 - Harris English 65-68, Rory McIlroy (NIR) 68-65, Dustin Johnson 71-62
134 - Ryan Palmer 67-67, Henrik Stenson (SWE) 71-63, Brendon de Jonge (ZIM) 67-67, Matt Kuchar 67-67, Justin Rose (ENG) 70-64, Nick Watney 68-66, Keegan Bradley 68-66
135 - Ryan Moore 68-67, Hideki Matsuyama (JPN) 72-63, Bubba Watson 65-70, Sergio Garcia (ESP) 70-65, Brian Harman 66-69, Bill Haas 68-67, J.B. Holmes 70-65, Rickie Fowler 69-66, Brendan Steele 68-67, Kevin Chappell 66-69
136 - Tony Finau 72-64, Steven Bowditch (AUS) 70-66, Paul Casey (ENG) 67-69, Hunter Mahan 68-68, Cameron Tringale 72-64