Johnson, enjoying his best stretch of play since winning last year's Masters, made 10 birdies and no bogeys at the TPC-Summerlin course to follow up his victory at the Texas Open.
The TPC-Summerlin course traditionally yields low scores and Johnson took advantage of good conditions to play his first nine holes in 4-under 32. He then birdied the first five holes on his second nine.
Johnson missed only one green in regulation and needed just 26 putts. He shot 62-64 over the weekend to post his victory in San Antonio, his first since becoming the surprise winner of the 2007 Masters.
"It kind of feels like you're playing in a dome," Johnson said, referring to the calm conditions. "You throw some grass and it just falls to your feet."