Na had a flawless round of eight birdies at TPC Summerlin to move into a three-way tie for first at 12-under 130 with first-round co-leader Jhonattan Vegas (67) and Charlie Wi (66). It's the fourth 36-hole lead for Na, who has yet to win on the PGA Tour.
"I've been hitting the ball real well," Na said. "I was hitting the ball well going into the Playoffs. Unfortunately, I wasn't feeling well there. So, obviously I didn't have a good finish. I was just hoping to make some putts today because I was hitting the ball real well."
The round was delayed in the early evening due to lightning and was nearly completed, with only Fran Quinn left on the last hole to complete his round. He is one shot off the projected cut line at three-under and elected to finish his round at 10:45 a.m. (et) on Saturday.
After Quinn finishes, the third round will go off in threesomes from the first and 10th tees.
Vegas holed an 11-yard bunker shot for eagle at the 15th, while Wi had six birdies and a bogey. Vegas, a tour rookie, is looking for his second win of the season, while Na and Wi are winless on the PGA Tour.
Tim Herron (66), Kris Blanks (65) and Brendan Steele (65) share fourth place at 11-under 131. The low round of the day went to Hunter Haas, who fired a 10- under 61 to tie a course record and get to 10-under overall.
Na did most of his damage on the last 10 holes, with birdies on seven of them.
He birdied only the third in his first eight, but back-to-back birdies from the ninth started him on his run down the back nine. Na had three straight birdies from the 12th, with a nine-footer on the 14th putting him at 10-under for the first time.
After parring the 15th, Na hit a five-foot birdie putt at No. 16 and a 12-foot birdie putt at No. 17 to gain a share of the lead at minus-12.
Vegas started on the back nine and parred the first five holes before the aforementioned eagle on No. 15. He followed with a bogey, but finished his first nine with an impressive 35-foot birdie putt at the 18th.
Around the turn, Vegas birdied the second and bogeyed the third to remain at 10-under before a 12-foot birdie putt at No. 7 and a two-putt birdie at No. 9 gained him a share of first once again.
"I felt like I putted really well today," Vegas said. "My ball striking wasn't as good as it was yesterday, and that's kind of why the round wasn't as good as yesterday. But my putting's been pretty well, which that's kind of what I've worked for."
Wi had a birdie and a bogey through the first eight holes before five birdies in an eight-hole stretch from the ninth. He hit a 14-footer for birdie at No. 9 to get started and added a 25-foot birdie putt at No. 11 to get to nine- under.
Back-to-back birdies from the 15th put Wi in first.
"I've only been here once before in six years, so I was pretty pleased with the way I played," Wi said. "I was here a few years ago, and the scores are so low, I was kind of scared just coming over here."
NOTES: The projected cut is at four-under 138. Quinn's tee shot on his last went into the rough...Defending champion Jonathan Byrd birdied four of his last five holes to make the cut at five-under...Haas' 61 is tied for the second-best round on the PGA Tour this season. Only Patrick Cantlay's 60 was better...The second-round leaders have gone on to win 10 of 40 stroke-play events this year.