Na flew up the leaderboard with a stellar front nine. He converted his first birdie opportunity at the par-4 third from 13 feet. The 21-year-old came right back to birdie the fourth from 16 feet at Omni Tucson National Golf Resort and Spa.
The South Korea native made it three straight birdies as he drained a 9-footer at the fifth to move to 14 under. Na closed a run of four straight when his birdie try from 12 feet at the sixth found the bottom of the cup.
Na bogeyed at the seventh when he three-putted from 32 feet, but bounced right back to birdie the eighth to get to 15 under. Na then dropped in a 10-foot birdie putt at the 11th.
He moved to 6 under for his round when his 14-foot birdie putt at the 14th fell into the cup. Na collected his second birdie in a row with a chip-in at the 15th to get to 18 under. He closed with three straight pars to share first.
'I played really solid,' said Na, who tied for second behind Phil Mickelson in Phoenix. 'I feel like my putter even feels better than Phoenix, so it's good. It's always nice to be in the lead.'
Ogilvy, a three-time runner-up on the PGA Tour, opened with a two-putt birdie at the par-5 second. The Australian came back with an 8-foot birdie at No. 5 to move to minus-15.
Ogilvy only needed a 7-iron to reach the par-5 10th green in two. He two-putted from 25 feet for birdie to get within two of Na's lead.
At the 663-yard, par-5 15th, Ogilvy was unable to get home in two with a 3-wood. He chipped to 4 feet and converted the birdie putt and made it two in a row with a 25-footer at the 16th.
He parred out to grab a piece of the 54-hole lead for the first time on the PGA Tour.
'I just kept trying to give myself short putts. It's all about giving yourself chances,' said Ogilvy, who tied for third at this tournament in 2001, his first event on the PGA Tour.
Darron Stiles posted a 5-under 67 Saturday to climb to 15-under-par 201. He was tied for sixth place with Brent Geiberger (68) and Joe Ogilvie (69).
Billy Mayfair managed an even-par 72 and is tied for ninth place with Scott Gutschewski (66), Danny Briggs (69), Arron Oberholser (67), Gavin Coles (71), Todd Fischer (67) and Steve Stricker (70). The group is knotted at 14-under-par 202.