Toms was joined atop the leaderboard by WGC-Accenture Match Play champion Geoff Ogilvy, Ryuji Imada and former Q-school medalist Mathias Gronberg.
Billy Mayfair, Brian Gay, Jeff Gove and Jason Schultz are one stroke further back at minus-4, as 14 players are within three strokes of the lead.
Toms began his round on the back nine of the Sunrise Course at Country Club of Mirasol. He stumbled to a bogey on his opening hole, but got up and down for birdie on the 12th.
The 2001 PGA Champion missed the green at the 13th and faltered to another bogey. Toms got that stroke back with a 25-foot birdie putt on the 15th. He made it two straight birdies as he ran home a 50-foot birdie effort on 16.
Toms three-putted for bogey on the 18th from the back of the green to make the turn at even-par. Around the turn, Toms ran home three straight 12-foot birdie putts from the third to jump to minus-3.
The 39-year-old pitched his third to the par-5 fifth to 18 feet. Toms rolled that putt in for his fourth birdie. He two-putted for birdie at the next to close a run of five straight birdies. Toms closed with three pars in a row.
'I started off kind of slow, but came back and ended up making a lot of birdies,' Toms said. 'I putted well and capitalized every time I hit a good shot.'
Imada, whose best tour finish is a tie for fifth at last year's Booz Allen Classic, opened with a 30-foot birdie putt on the 10th, his first. He sank a 15-footer for birdie at 12, but gave a stroke back with a bogey on No. 14.
The 29-year-old found a hazard on the 16th and that led to his second bogey. Imada quickly got back to minus-2 with an eagle on the 17th. He came right back with a 12-foot birdie putt on 18 to make the turn at minus-3.
Imada got to 4 under with a 12-foot birdie putt at the second. He missed a 12-foot par putt on four, but got that stroke back with a 6-foot birdie effort at the sixth. Imada birdied the seventh to grab a share of the lead and parred his final two holes to remain there.
'Conditions were very difficult,' Imada said. 'I heard Bob Estes talking about it. He said 'It was British Open conditions with a PGA Tour setup.' I thought that was kind of true. It's only Thursday, I just wanted to shoot somewhere in red numbers today.'
Ogilvy also played the back nine first on Thursday. He was 1 under for those nine holes with an eagle, a double-bogey and a birdie. Ogilvy parred the first four holes of the front nine before sinking a birdie on the fifth.
The Australian then hit the shot of the day at the par-five sixth. Ogilvy holed his 8-iron second shot from 180 yards out for a double-eagle that jumped him into a share of the lead.
Ogilvy looked like he was going to finish one back after a bogey on the eighth, but he birdied nine from 22 feet out to end at minus-5.
'I got a big bonus on six with the double-eagle,' said Ogilvy. 'I made a couple of nice up and downs on the front nine. All in all, an eagle and a double-eagle in one round is a real bonus.'
Gronberg got off to a good start as he birdied the first from inside 8 feet. He got up and down for birdie on the fifth from in front of the green, then was able to birdie the par-5 sixth from over the green to get to minus-3.
The Swede knocked a 7-iron to 4 feet at the eighth to setup his fourth birdie. Gronberg blasted out of a greenside bunker at the 12th and nearly holed the shot for eagle. He settled for a tap-in birdie that gave him a share of the lead.
Gronberg, who turns 36 on Sunday, three-putted for bogey on the 16th, but atoned for that error with a two-putt birdie on 17.
Shaun Micheel, the 2003 PGA Champion, posted a 3-under-par 69 Thursday. He shares ninth place with Dudley Hart, Scott Hend and John Cook. Davis Love III leads a group of six players one shot further back at minus-2.