Sigel, the two-time U.S. Amateur champion who won the last of his six Senior PGA Tour titles in 1998, had a 3-under 141 total on the Coyote Creek course.
'I would say that 73 is a good score today, especially with the way I putted,' said Sigel, who returned to the tour last June after a seven-month layoff following operations on both shoulders.
With the wind gusting to 35 mph and temperatures in the low 50s, no players broke par Saturday, the first time that has happened on the senior tour since 1997.
Sixty-two-year-old George Archer, from nearby Gilroy, shot a 74 to join Ed Dougherty (72), Bob Gilder (75) and Dana Quigley (75) at 142. Dougherty's 72 matched Bobby Wadkins, five strokes back at 146, for the best round of the day.
'I knew this was going to be a hard day and thought that par might be a real good score,' Dougherty said.
The 6-foot-6 Archer is seeking his 20th senior title.
'I'm like a big tree that gets blown around in winds like this,' Archer said. 'But I'm happy to be here.'
Quigley is playing in the 160th consecutive tournament and the 174th straight event in which he has been eligible, three short of the senior record set last year by Mike McCullough.
'Making par on a hole today is like making an eagle on any other day,' Quigley said.
Senior newcomer Fuzzy Zoeller (73) and Tom Wargo (76) were two strokes back at 143. Zoeller is 53rd on the money list with $54,912 in five senior starts. He made five cuts in 15 PGA Tour starts last year, earning $38,530.
Canada's Dave Barr, playing his first senior tournament, shot a 74 for a 146 total. Barr, a two-time winner on the PGA Tour, turned 50 on March 1.
Defending champion Hale Irwin shot a 79 to drop eight strokes back at 149. Irwin won the Toshiba Senior Classic last week in Newport Beach for his record 34th senior title.
The winner will receive $210,000 from the $1.4 million purse.
Full-field scores from the Siebel Classic at Silicon Valley