'It's hard to follow up a crazy round with a good one,' Letzig said. 'I tried to stay aggressive.'
Letzig entered the week 26th on the list, a spot away from earning a PGA Tour card for next season. The 27-year-old former New Mexico player had a tournament-record 16-under 126 total on the Barona Creek course.
'I know I'm good enough to play on the PGA Tour,' Letzig said. 'If it doesn't happen now, it will.'
Richard Johnson, already safe at No. 6 on the money list, was second after a 64.
'It's pretty much stress-free,' Johnson said. 'I'm having a good time. I feel fresh and am enjoying myself.'
Roland Thatcher, the money leader, also shot a 64 to join PGA Tour outsiders Jim McGovern (66), Tom Scherrer (65), B.J. Staten (66) and Tjaart van der Walt (68) at 11 under. Scherrer began the week 27th on the money list, while Staten was 30th, McGovern 45th and van der Walt 49th.
For the second straight day, fog delayed the start of play.