Justin Thomas shot a course-record 61 to take the lead at the halfway stage in the PGA Tour's CIMB Classic at Kuala Lumpur Golf Club.
The American carded nine birdies and an eagle in his 11-under-par round to move to 15 under for the tournament, one stroke ahead of compatriot Brendan Steele.
Ireland's Padraig Harrington shot a second round 72 to fall back to 45th overall after an encouraging 68 on Thursday had left him firmly in the hunt. Stunted by a quadruple bogey on the 11th, and there was a bogey on the fourth too, his birdies on the first, third, fifth, 10th and 14th holes were cancelled out.
Thomas though was quickly into his stride, picking up a shot at the first and two more with a three at the 503-yard third.
Two more birdies immediately followed and another at the ninth meant he was out in 30.
Five birdies in six holes after the turn, the pick of them via a wonderful approach at the difficult 12th, led to thoughts of a 59 but a long birdie putt at 17 slid just by and he had to settle for matching his career-best round.
He said: “I didn’t really think about (59) all day, having to make birdies to do it, until I only had two holes left and I had to birdie the last two.
“It’s really fun, it doesn’t happen too often in this sport, and I just made it really easy on myself. It was about as easy an 11 under as you could shoot.”
Steele was almost as impressive with a 63 which saw him chip in to match Thomas’ eagle at the third and add seven birdies.
Scott Piercy, who led after an opening 62, could only manage 69 on Friday but remained only two shots off the lead alongside Spencer Levin and Japan’s Hideki Matsuyama, who carded 64 and 66 respectively.
Stewart Cink was 12 under after a 64, with Brian Harman and Kevin Na at 11 under. Australia’s 2013 Masters champion Adam Scott was 10 under alongside American pair Jason Gore and Troy Merritt.
Spain’s Sergio Garcia and Germany’s Alex Cejka were the leading Europeans at seven under, with England’s Paul Casey a further shot back.
Ernie Els’ three-under 69 featured two of the most contrasting putts imaginable as he holed a superb 35-foot uphill effort at the sixth but missed from less than three feet at 18.
