Na eagled the par-5 first hole Friday on the way to an 8-under 62, his third score at least that good in the past six rounds on the cozy course made famous by Ben Hogan. Na, tied for second at 8 under with first-round leader Tony Finau, trailed Jonas Blixt by one halfway through Colonial.
After opening with a 62 and closing with a course record-tying 61 to finish fourth last year, Na followed the eagle with six birdies in a bogey-free round after being happy to shoot par 70 on a windy afternoon in the first round.
"One of those golf courses I look forward to coming to," said Na, a two-time PGA Tour winner who puts Colonial in his top three along with Riviera and Hilton Head. "Fits my game. You've got to take advantage of those weeks because there is not too many golf courses like this on tour anymore."
Blixt, a three-time winner playing with Na, holed out from 132 yards for eagle on No. 17 and shot 64 to reach 9 under. Finau, playing the back nine first, started with nine straight pars before three birdies and a bogey on his final nine for a 68.
Local favorite Jordan Spieth, a shot off the lead to start the day, shot 70 and was four behind Blixt. Defending champion Justin Rose, the highest-ranked player in the field at No. 3, shot 67 and was 1 over, one stroke above the cut line.
Rory Sabbatini, the 2007 Colonial champion, shot 66 and was alone in fourth at 6 under. Jim Furyk, the 2003 U.S. Open champion who hasn't won in four years, shot 66 and was with Spieth and three others at 5 under.
Blixt, a three-time tour winner, had a little more success navigating the wind than Na in the first round, shooting 67. Both were thinking more about hanging on while hoping to make a move in the second round.
Na didn't waste any time, hitting his second shot to 3 feet for the easy eagle before three birdies on putts of at least 30 feet. After Blixt went up two shots with his pitching wedge from 132 yards at 17, Na pulled within one with a closing birdie when his approach settled inside 5 feet.
"Well, I was trying to do it, so ..." Blixt said about his eagle, the 35-year-old Swede pausing for effect without smiling.
"Nah, so the last two times I played the hole it's been the same kind of wind. We've been thinking it's like left-to-right wind or almost into us, so today I just played more like a little downwind."
Jason Dufner got to 8 under with four straight birdies and a 25-foot putt to save par. But the two-time Colonial runner-up missed a short birdie putt at No. 6, his 15th hole, and bogeyed three of the last four for a 68 that left him at 5 under.
Spieth made birdie putts of 50 feet on No. 10 and 46 feet at 12, giving him three putts of more than 40 feet in the same tournament for the first time after making a 46-footer in the first round. But the three-time major winner missed three par putts under 10 feet among his five bogeys.
"I thought today was average; I thought yesterday was spectacular," Spieth said "Today I missed maybe an 8-footer and a couple 5-footers, but then I made a couple long ones to make up for it. They were kind of misreads. They weren't bad strokes. That's the difference."
Rickie Fowler missed the cut by one shot at 3 over, ending a streak of 21 straight cuts made. It was tied for the second-longest active streak with Tommy Fleetwood and Hideki Matsuyama, one behind Jason Kokrak (22).
Other than the 16th-ranked Finau, Colonial has been unkind to the eight players in field among the top 20 in the world rankings. Francesco Molinari, ranked seventh, and Rose are the only others playing on the weekend. Molinari joined Rose at 1 over after a double bogey on his last hole.
No. 11 Jon Rahm shot 71 and missed the cut at 6 over after finishing in the top five in both of his first two Colonials the past two years.
Eighth-ranked Bryson DeChambeau (4 over) and No. 9 Xander Schauffele (6 over) missed along with Fowler (10th). Paul Casey, ranked 13th, withdrew because of flu-like symptoms after opening with a 69.
Two-time Colonial winner Zach Johnson shot 75 to finish 7 over, missing the cut for the second straight year after playing on the weekend in his first 12 Fort Worth appearances.
Brian Harman put himself under par for the tournament on his last hole when his approach shot at 9 bounced off the grandstand behind the green and rolled within 2 feet of the hole. He made the birdie putt and handed the ball to a fan sitting not far from where it caromed.
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