Mexico City - Bryson DeChambeau put on a putting clinic on the way to an eight-under par 63 and a one-shot lead in the WGC Mexico Championship over Erik van Rooyen and Patrick Reed.
America's DeChambeau rolled in 143 feet of putts as he built a 36-hole total of 11-under par 131 at Club de Golf Chapultepec.
Former Masters champion Reed was also red-hot on the greens on the way to a 63 that put him at 10-under alongside South Africa's Van Rooyen - who had nine birdies without a bogey in a 62 on his 30th birthday.
World number one Rory McIlroy came alive late on the way to a two-under par 69 that put him two off the lead alongside Japan's Hideki Matsuyama and American Justin Thomas.
Matsuyama was 11-under for the tournament after posting nine birdies in his first 15 holes, but two late bogeys saw him sign for a seven-under par 64.
Thomas was atop the leaderboard at 10-under after his eagle at his 10th hole of the day - the first - but eventually signed for a 66.
DeChambeau's fireworks on the greens included a 46-foot birdie putt at the seventh, which followed a 26-footer at No 6.
DeChambeau had teed off on 10 and rolled in a six-footer for his first birdie of the day at 11. He didn't miss a putt from within 10 feet and strung together four birdies in a row from the 18th through the third.
"It was a lot of fun," said DeChambeau, a three-time winner on the PGA Tour.
"When you have days like that you can't help but smile out there. Making those putts the way I did, striking the ball like I did, it was surely a joy out there."
DeChambeau said his 13-foot birdie putt at the 18th was the real momentum-builder.
"When this putt rolled in perfectly I just felt super-confident on the greens," he said.
The monster on number seven - which saw him tie his career best with nine birdies in the round - was just a bonus.
"I just threw my hands in the air," DeChambeau said. "I mean, come on - who thinks I'm going to make this one?"
Reed was similarly impressive with the putter, posting a burst of four straight birdies on the front nine and notching five more birdies coming home.
Van Rooyen, who won his maiden European Tour title at last year's Scandinavian Open, admitted he was feeling "really old" when he woke up on his 30th birthday.
The mood was more celebratory when he walked off 18 having nabbed his ninth birdie of the day.
"What a way to kick off the 30s," he said, "little bit of a gift to myself."
McIlroy never quite found his way onto the birdie bandwagon.
The overnight leader by two, McIlroy was one-over through nine and didn't make his first birdie of the day until the 12th.
He promptly gave the shot back, but birdied 14 to get himself back to even par for the day.
With a 16-foot birdie at 16 and a 24-footer at 17 McIlroy kept himself in the hunt for a title that saw him complete his collection of the prestigious World Golf Championships titles.
He won the WGC-HSBC Champions in Shanghai in November to go with the WGC Match Play he won in 2015 and the WGC Invitational he nabbed at Firestone in 2014.
Leading second round scores on Friday in the World Golf Championships Mexico Championship at Club de Golf Chapultepec (USA unless noted, par-71):
131 - Bryson DeChambeau 68-63
132 - Erik van Rooyen (RSA) 70-62, Patrick Reed 69-63
133 - Hideki Matsuyama (JPN) 69-64, Justin Thomas 67-66, Rory McIlroy (NIR) 65-69
137 - Sebastian Munoz (COL) 71-66, Tyrrell Hatton (ENG) 69-68, Paul Casey (ENG) 69-68
138 - Corey Conners (CAN) 68-70
139 - Lee Westwood (ENG) 69-70, Kevin Na 71-68, Matthias Schwab (AUT) 71-68, Billy Horschel 68-71, Bubba Watson 67-72, Louis Oosthuizen (RSA) 68-71, Tommy Fleetwood (ENG) 70-69, Gary Woodland 70-69
140 - Zach Murray (AUS) 71-69, Ryan Fox 72-68, Abraham Ancer (MEX) 70-70
141 - Danny Willett (ENG) 73-68, Jon Rahm (ESP) 72-69, Zander Lombard (RSA) 73-68, Shane Lowry (IRL) 72-69, Lanto Griffin 72-69, Im Sung-jae (KOR) 69-72
142 - Collin Morikawa 72-70, Justin Harding (RSA) 71-71, Matthew Fitzpatrick 72-70, Adam Scott (AUS) 74-68, Rafa Cabrera Bello (ESP) 71-71, Kevin Kisner 73-69, Matt Kuchar 75-67, Branden Grace (RSA) 71-71