KAPALUA, 11 Jan 2015 (AFP) - Johnson's effort gave him an 11-under par total of 135. He was joined atop the leaderboard by first-round leader Russell Henley, South Korea's Bae Sang-Moon and Jimmy Walker.
Henley carded a three-under par 70, Walker signed for a 68 and Bae had four birdies without a bogey in a four-under 69 on the Plantation Course at Kapalua.
The last three winners of the tournament, limited to the previous season's tournament winners, have had at least a piece of the lead after 36 holes.
Charley Hoffman and Japan's Hideki Matsuyama both fired seven-under 66s.
They were in a group sharing fifth place, one shot behind the leaders on 136.
They were joined there by Brendon Todd (67), Patrick Reed (69) and Robert Streb (69).
Scott Stallings fell out of a tie for the lead as he finished with back-to-back bogeys in a three-under 70. He was alone on 137.
Matt Kuchar was a further stroke back after a 70 for 138.
Reigning Masters champion Bubba Watson, the highest-ranked player in the field at fourth in the world, carded a 69 to head a group on 139 that also included Ben Martin and Australians Jason Day and John Senden.
Johnson is seeking to become the first repeat winner of the Tournament of Champions since Australia's Geoff Ogilvy in 2009 and 2010.
Johnson has also won the US tour's Sony Open in Hawaii, in 2009, and said he enjoys the challenge of the island winds.
"When it comes to execution with the wind and trajectory control, they're very similar," he said of the conditions at the two Hawaiian tournaments. "I like that kind of golf."
Johnson hit all 15 fairways and all 18 greens in regulation.
"It was solid," said Johnson, whose only blemish was a three-putt bogey at the par-three eighth. "I was trying to go the week without a three-putt, but I failed on that one. So we'll try to leave it to one three-putt."
Playing partner Nick Taylor of Canada said Johnson's ability to put the ball in the right spot was key, something Johnson's no doubt learned in seven prior appearances in the event.
"He definitely would keep it under the hole, which is big," Taylor said. "A lot of times today I was down grain, downhill, was kind of defensive all day. He was definitely under the hole and giving himself way more aggressive putts."
Leading second-round scores on Saturday in the US PGA Tour Tournament of Champions (USA unless noted, par-73):
135 - Zach Johnson 68-67, Jimmy Walker 67-68, Russell Henley 65-70, Bae Sang-Moon (KOR) 66-69
136 - Hideki Matsuyama (JPN) 70-66, Charley Hoffman 70-66, Brendon Todd 69-67, Patrick Reed 67-69, Robert Streb 67-69
137 - Scott Stallings 67-70
138 - Matt Kuchar 68-70
139 - Jason Day (AUS) 70-69, Bubba Watson 70-69, John Senden (AUS) 68-71, Ben Martin 67-72
140 - Brian Harman 70-70, J.B. Holmes 69-71
141 - Ben Crane 74-67, Geoff Ogilvy (AUS) 72-69, Ryan Moore 71-70, Noh Seung-Yul (KOR) 71-70, Camilo Villegas (COL) 71-70, Matt Jones (AUS) 69-72
142 - Billy Horschel 72-70, Hunter Mahan 71-71, Kevin Streelman 69-73, Steven Bowditch (AUS) 69-73, Nick Taylor (CAN) 69-73
143 - Chesson Hadley 70-73
144 - Matt Every 73-71, Angel Cabrera (ARG) 71-73, Chris Kirk 68-76
145 - Tim Clark (RSA) 70-75
147 - Kevin Stadler 74-73