The 42-year-old has a history at this event, having won back-to-back titles in 2008 and 2009, the first two times he competed in it.
“I felt really good coming into the week,” said Johnson, who also won the 2007 Masters crown. “I hit solid shots.
“I was fixated on keeping the peddle down. I was striking it well. My driver was key. The confidence is there.”
Under cloudy, windy conditions in San Antonio on Friday, he rolled in six birdies and an eagle to tie for the lead at nine-under 135 with fellow American Ryan Moore, who fired a five-under 67. They will be in the final group in Saturday’s third round.
They are one stroke ahead of Andrew Landry and Grayson Murray, who shot 67 and 69, respectively.
Ben Crane (66), Martin Laird of Scotland (65) and Canada’s David Hearn (68) are tied for fifth at six-under, three shots adrift of the leaders.
Both Johnson’s win here came on a different course, LaCantera Golf Club, but the TPC San Antonio suits him just fine.
He is one of just four winners in tournament history, dating to 1922, to successfully defend the title, joining Bill Mehlhorn 1928-29, Arnold Palmer 1960-62 and Justin Leonard 2000-01.
The 2015 British Open winner holed out of a greenside bunker at the fifth hole for an eagle-two, his second eagle of the week. On the par-four 15th he hit his 173-yard approach to 15 feet then sank the putt for his fourth straight birdie.
Johnson has made the cut in all 12 starts this season as he aims for his 13th win on the USPGA Tour.
He said if there is more wind in Saturday’s round it is not going to throw him off.
“I am not afraid of the wind,” Johnson said. “I played well and relished in the wind — what do you call it The Open Championship or some of those other tournaments I played in. It doesn’t matter. It is hard for everybody if there is wind.”
Moore shot his second straight bogey free round on Friday after posting a 68 on Thursday.
“My distance control has been great and really my ball-striking has been really nice the last few weeks,” Moore said. “The putter just kind of hasn’t been co-operating.”
Except on the sixth and 17th holes when he rolled in birdie putts from more than 14 feet.