He posted a 13-under 200 total, one stroke ahead of fellow American Morgan Hoffmann (71), who sank a 10-footer at the par-four 18th to salvage bogey after yanking his drive into a rocky lie in a desert hazard.
Kevin Na (68), Jimmy Walker (69) and Chad Campbell (70), all tour winners, are two shots behind, while German Alex Cejka, boosted by a hole-in-one with a six-iron from 212 yards at the 17th, is among a group of three adrift.
Stegmaier, 32, who has plied his trade on almost every mini-tour in the United States, was playing so badly in September that he thought about quitting.
Without any other appealing employment prospects, however, he decided to persevere on the secondary Web.com Tour.
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Suddenly he found form and five weeks later earned his card to the main tour. He seems unfazed by his lofty position.
“I felt really comfortable,” he told Golf Channel. “It’s weird. I would have thought I’d be a lot more nervous but I just feel I belong in this position and I felt really good out there.
“I drove it really well. I feel like I’m really good at staying patient. I play conservatively, so I usually have a lot of 20-30 footers, a lot of two-putt pars, which I knew was going to be good today, with the greens being firmer. It was a pretty easy day all things considered.”
Hoffmann, meanwhile, made his move late with four birdies in five holes from the 13th, before giving one back at the last.
"I'm happy to walk away with a bogey," said the 26-year-old who finished 26th in the tour standings in 2013-14. "It was a very up-and-down rollercoaster round."
Na, who lost a playoff at the season-opener in California last week, continued his good form to lurk within striking distance again.
The Las Vegas resident identified the reason scores have not been lower in an event that usually is a birdie shootout.
“This was unexpected, because in the Wednesday pro-am greens were really soft,” said the 2011 champion.
“We thought 20-plus-under was going to win. The golf course seemed like it changed overnight. Scores are reflecting how firm these greens are.”
(Reporting by Andrew Both in Cary, North Carolina; Editing by Ian Ransom)
