(Reuters) - American Bryson DeChambeau was giddy with joy after charging into a one-stroke lead in the second round at the WGC-Mexico Championship on Friday as overnight pacesetter Rory McIlroy's title bid stalled.
Physics major DeChambeau solved the high altitude puzzle, putting with precision and making seven birdies in an eight-hole stretch en route to an eight-under-par 63 in ideal conditions at Club de Golf Chapultepec in Mexico City.
At 11-under 131, he headed South African Erik van Rooyen, who matched the course record with a nine-birdie 62 on his 30th birthday, and American Patrick Reed (63).
Japan's Hideki Matsuyama (64) and American Justin Thomas (66) trailed by two strokes, while Northern Irishman McIlroy (69) fell three behind after a frustrating afternoon, though it would have been more if not for a late rally.
"When you have days like that you can't help but smile out there," said a beefed-up DeChambeau, who has added about 30 pounds (14 kilograms) of rippling muscle over the past year in an effort to increase his power.
But it was a silky putting touch that was most responsible for his sizzling score, not least the 45-footer that he sank at his 16th hole, the par-three seventh.
"I just threw my hands up in the air. I mean, c'mon," said the five-times PGA Tour winner, who has also won on the European Tour.
"Making those putts the way I did, striking the ball like I did, it was surely a joy out there.
"The confidence has got to be high and it is high. Everything's going pretty well, firing on all cylinders."
The same could be said for van Rooyen, who has chipped in three times already, twice on Thursday and once on Friday.
"When you shoot nine-under everything's going well," he said. "What a way to kick off the 30s."
Reed matched van Rooyen's nine birdies, though the former Masters champion also added a bogey.
"The putter was working," said Reed, as happy with his green-reading as his stroke. "What you see is not always what you get here."
Matsuyama might have enjoyed a share of the halfway lead but for two late bogeys, while Thomas could not build on a brilliant six-under stretch over five holes from his sixth.
Overnight leader McIlroy endured a miserable day on the greens, at least until he sank a couple of birdies at the 16th and 17th holes.
He also was poor on the par-fives, parring all three.
"I made a couple of nice putts coming in. I guess my patience was rewarded a little bit," McIlroy said.
(Reporting by Andrew Both in Cary, North Carolina; Editing by Ken Ferris)