Steele, whose only PGA Tour victory came at the 2011 Texas Open, birdied seven of his last eight holes for a red-hot homeward nine of seven-under 29 to set a sizzling pace in the season-opening event on the U.S. circuit's 2015-16 schedule.
Venezuela's Jhonattan Vegas carded a 64 while American rookie Harold Varner III and Britain's Martin Laird returned 65s but Steele will certainly be keeping a wary eye on world number seven Rose (67) and third-ranked McIlroy (68).
"I was really comfortable," Steele, 32, told Golf Channel after racking up nine birdies in a bogey-free display in the opening round.
"I'm just trying to stick into my process and, as cliched as it sounds, just kind of get into every shot as much as I can and not really think about the results. The golf course is in perfect shape, just the right amount of bounce on the greens.
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"They're not too soft, not too firm. They're rolling perfect. Everything was great," said Steele, who grew up in the small Californian town of Hemet where was neither a golf course nor a driving range.
RISING ROSE
Englishman Rose, who won his first major title at the 2013 U.S. Open, mixed six birdies with a lone bogey to vault up the leaderboard.
"It went well," said Rose, back in action on the PGA Tour just two weeks after tying for second place at the Tour Championship, the final event of the 2014-15 season.
"A couple of guys are going lower than that but for the first round of the season ... it was a nice way to get things going."
McIlroy, making his first trip to the idyllic wine country of California's Napa Valley, bogeyed his fourth hole of the day before rebounding with five birdies to climb into contention.
"I felt like I played pretty well," said the Northern Irishman, 26, who won three tournaments earlier this year before being sidelined for almost two months after rupturing an ankle ligament while playing soccer with friends on July 4.
"I got off to a bit of a slow start this morning but gradually got into the round and started hitting some better shots and giving myself plenty of chances.
"I didn't convert many of them but still a pretty solid score and in good position going into the next three days."
A notable absentee this week is last year's winner, Bae Sang-moon, due to a requirement for him to complete two years of military service in his native South Korea.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Greg Stutchbury)
