England's Casey fires back-nine 27 at PGA event
Paul Casey of England plays a shot on the fifth hole during the first round of the HP Byron Nelson Championship at the TPC Four Seasons Resort on May 15, 2014 in Irving, Texas - by Sam Greenwood
The 36-year-old Englishman fired a second-round 63, seven-under par, to stand on six-under 134 after 36 holes, sharing second in the clubhouse with much of the field still on the course.
Casey became only the eighth player in US PGA history to fire 27 for nine holes, one off the tour record 26 fired by American Corey Pavin on the front nine in the first round at Milwaukee in 2006.
"I had no concept of what I was doing," Casey said.
Casey's lone US PGA title came at the 2009 Houston Open, but he has 13 other global triumphs, including last year's Irish Open.
Casey took bogeys at the third and par-3 fifth holes and although he pulled one back with a birdie at the par-5 seventh he closed the front nine with another bogey.
Then came his blazing back nine.
Casey sank a six-foot birdie putt at the 10th and followed with a 24-foot birdie putt at 11.
After finding a greenside bunker at 12, Casey saved par from 13 feet and followed with a birdie from 13 feet at the par-3 13th hole.
Casey added birdie putts from nine feet at 14 and four feet at 15 before making an eagle at the par-5 16th, dropping his second shot 32 feet from the cup and then dropping in the putt.
He followed by parring the par-3 17th and closing with a birdie, sinking a five-foot putt at 18.
"The seal was broken when I got to 10," Casey said. "It just spiraled from there."
"I like to think I would be pretty good at shooting low rounds of golf through the past, but certainly nothing like that."
Casey's prior low score over nine holes in a US PGA event was a 30, which he achieved twice, most recently at New Orleans last month.