Sigel shot 64 to move to 14-under; three shots clear of John Jacobs (66). Larry Nelson (65), Jim Thorpe (65), Allen Doyle (66), Bobby Wadkins (69) and Joe Inman (69) are tied for third place at 10-under.
Wadkins, making his tour debut, and Inman shared the 18-hole lead - as did J.C. Snead, who is now nine back after a 74.
Sigel is a six-time winner on the Senior circuit, but has gone winless over the past three seasons.
The back-to-back U.S. Amateur champion (1982-83) was one off the overnight lead. After a par at the 1st, he birdied hole Nos. 2-7 at the Meadow Brook Club. He also birdied the 10th, 11th and 14th holes; however, the 57-year-old bogeyed the par-3 15th to finish the day at minus-14.
Full-field scores from the Lightpath Long Island Classic