Las Vegas local Na finished with a 10-under 61 on a day of low scoring.
The South Korean-American ended the day with a 22-under total of 191, which was a 54-hole record at the event he previously won in 2011.
Na began with a pair of birdies on the first and second and kept his cool to nail a 22-foot putt on the fifth and save par.
Cantlay notched eight birdies in his first 16 holes but got stuck in a bunker on the 17th before closing out the final hole with a birdie.
Russell Knox of Scotland was Britain's best performer, moving up 20 places to 15th on 13 under after shooting a 65.