Matt Bettencourt dropped shots at his closing two holes to give up the outright lead after round two of the Reno-Tahoe Open.
Starting on the back nine, by the time he reached the eighth tee Bettencourt had moved from six-under to 12-under-par, and looked certain to head the field at the tournament's halfway stage.
However he made five at the 464-yard par-four eighth, and added a six at the 616-yard par-five ninth, so had to settle for a round of 68 to follow up the opening 66 which had made him the first-round leader.
That meant the 35-year-old, who tied for fifth at the Memorial Tournament and 10th at the US Open in 2009, shared the lead with fellow American Robert Garrigus.
Garrigus produced a sparkling 65, with seven birdies and no dropped shots, matching the lowest round of the day.
The other 65 came from Len Mattiace who shot 78 on Thursday but recovered well enough to make the cut with comfort, moving to a one-under aggregate.
Australians Aron Price, Rod Pampling and Jarrod Lyle are seven shots back at three-under heading into the weekend, while Steve Elkington, Mark Hensby and Stuart Appleby are a further stroke back.
Garrigus is aiming for his first PGA Tour victory but should have had one in the bag already, frittering away a three-shot lead on his final hole at the St Jude Classic last month, before losing to Lee Westwood in a play-off.
John Mallinger moved into third place on a leaderboard dominated by Americans, with a 67 taking him to eight-under, while Bob Heintz, Bill Lunde, John Merrick, Kevin Stadler were a shot further adrift.
Next in line, on six-under, were two of the biggest names in the field.
Chad Campbell, runner-up at the Masters last year and PGA Championship in 2003, carded a second successive 69 to be level with former Open Championship runner-up Chris DiMarco, who shot 71.