The Englishman signed an unblemished card for the second successive day at the opening event of the 2022-23 PGA Tour season.
Willett, the 2016 Masters champion, finished with back-to-back birdies for a halfway score of 132 to join Max Homa on 12 under par.
"Bogey-free is probably the most impressive," he said after the round.
"We've not hit it amazing, we've hit it really good and this place still kind of jumps up.
"The rough is hit and miss and with the greens being firm as they are to go bogey-free is really good."
Willett is trying to make the most of his lucky break this season, after managing to hold onto his PGA Tour card only after a number of LIV Golf rebels were removed from contention on the points list.
"Yeah, we kind of got handed a lifeline with the guys leaving," Willett said. "We kind of had to reassess things and decided we'd press on and play a little bit more this fall over here and really try to get some points up early."
Defending champion Homa made one eagle and four birdies in his 67 at Silverado Country Club.
"The course fits my eye," said the American.
"I hit a lot of wedges today and I've been hitting the wedges really well, so when I get a lot of wedges from fairways like these, I feel like I can attack the pins."
First-round leader Justin Lower and South Korea's An Byeong-hun are two shots back, with American trio Matt Kuchar, Sahith Theegala and Taylor Moore another two strokes adrift.
English pair Ben Taylor (six under) and Matt Wallace (three under) and Scotland's Russell Knox (three under) made the cut, with former world number one Jason Day among those to miss out after rounds of 74 and 73.