Maverick McNealy soared to the top of the leaderboard at the halfway stage of the Fortinet Championship, but John Rahm's PGA Tour season debut ended in the world number one missing the cut.
McNealy earned a two-stroke lead following the second round of the 2021-22 season opener at Silverado Country Club, where the 25-year-old American carded an eight-under-par 64.
It is McNealy's lowest opening 36-hole score (68-64) on the PGA Tour.
However, Spanish star Rahm failed to qualify for the weekend after back-to-back rounds in the 70s in Napa, California.
Tuning up for the Ryder Cup, Rahm – who missed Wednesday's pro-am due to a stomach ailment, having placed second in the FedEx Cup play-offs – never got going, an opening-round 72 followed by a 71 as he finished one under, below the three-under cut line.
"I get to rest a couple extra days and be able to figure out what's going on with my swing, which technically is not really anything bad," said Rahm, who recorded his 13th missed cut in his 113th PGA Tour start, with his last missed cut at this year's Wells Fargo Championship.
"It's just I think a lot of those swings were made to look worse because of how tough it is out there."
Beau Hossler (64) and Mito Pereira (67) are tied for second and two shots adrift of McNealy heading into Saturday's third round, while Troy Merritt (68), Will Zalatoris (67) and Bronson Burgoon (67) are a stroke further back at nine under.
"Naughty, naughty, naughty."— PGA TOUR (@PGATOUR) September 18, 2021
Phil navigates the aftermath of a volunteer picking up his ball. pic.twitter.com/PfgozGAJXx
Rookie David Lipsky's second-round 64 was a nine-stroke improvement on his first round and a career-low round that included nine birdies, the most he has managed in a single round on Tour.
Lipsky is seven under through 36 holes, alongside the likes of Tom Hoge (66) and Peter Malnati (66), while Masters champion Hideki Matsuyama is a shot back following his three-under-par 69.
Six-time major champion Phil Mickelson posted a 69 to be tied for 24th and seven shots off the pace.