Phil Mickelson and Chesson Hadley finished three shots behind.
A year ago at Silverado, he birdied the final three holes to overcome a four-shot deficit and beat Patton Kizzire by a stroke for his second PGA Tour title.
John Daly, the two-time major victor who won his first PGA Tour Champions title in May, closed with a 79 to tie for 72nd at 5 over.
Lucas Glover, Chez Reavie, Emiliano Grillo and Jamie Lovemark were two shots back at 67. But a birdie at 16 moved him to 14 under and a two-shot lead.
Steele, who has two wins on the Tour, recorded five birdies in a six-hole stretch from number 13 to number 18.
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This certainly does put more pressure on Carlos Sainz Jr .to perform in better equipment. "He has always shown great human qualities and we wish him the best for the rest of his career".
Beginning two shots off the pace, Steele posted back-to-back birdies from the fourth and added a six-foot gain at the ninth to reach the turn in 33. "I knew the weather was going to be windy and it seems Sunday is always the hardest day on the PGA Tour for whatever reason".
"I'm proud of the way I played today". He carded one more birdie at number six to cap his bogey-free round.
Thomas previously won the PGA of America award as player of the year, which is based on points.
There was little joy for the four Australians in the early stages of the opening event of the 2017 - 2018 PGA Tour season, the Safeway Open at the Silverado Resort and Spa in Napa in California. I had a really good ball-striking day.
He said: "Let's take a moment to admire the fact that I just hit a fairway". Thomas made the choice easy when he closed with a 66 at East Lake to finish one shot behind in the Tour Championship, which allowed him to win the FedEx Cup and its $10 million bonus.
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He practiced this past week on a limited basis but did not speak to reporters because he was still in the concussion protocol. Adams passed the final test shortly before the Packers boarded their plane for Dallas on Saturday afternoon.
He ended joint-third with Chesson Hadley at 12 under - the 47-year-old's highest finish in a Tour event since being the runner-up at the 2016 Open Championship.
Steele won last year's Safeway Open in Napa, shooting a 65 in the final round. Tyler Duncan, who led the event after the third round, finished tied for fifth with Graham DeLaet at 11-under par.
Finau's round consisted of an eagle-3 on No. 5, birdies on Nos.
Sangmoon Bae carded a one-over 73 on his return to the PGA Tour after serving military service in his native South Korea, dropping four shots in a row but scoring birdies on the 12th and 18th.
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He later resurfaced in northern Syria as the commander of a group of foreign fighters and became a senior leader within IS. The three countries agreed in May to be guarantors of a cease-fire to help end the six-year civil war in Syria.