Tewell fired a 5-under-par 67 to move to 11-under for the tournament, three shots removed from Mike McCullough (69), Tom Wargo (69) and Larry Nelson (64).
Allen Doyle is four back after a round of 66; while Bruce Fleisher (67), Hale Irwin (68) and Gil Morgan (69) are all giving chasing at 6-under-par.
Tewell started the day with a one-shot lead at 6-under. He stayed on that number with five successive pars, until he birdied two of his final four holes on the front nine.
After making the turn at 8-under, the 2000 Rookie of the Year added three more birdies to his card, including one at the home hole.
After a three-win season a year ago, Tewell is in search of his first title in 01; and his second major championship overall. The 51-year-old made the PGA Seniors Championship his maiden tour victory last year.
Five shots back, Irwin is trying to complete the career Grand Slam on the Senior Tour. Hes won the other three majors ' the U.S. Senior Open, PGA Seniors Championship and Ford Senior Players Championship ' at least once.
Jack Nicklaus is the only player to win all four majors on the Senior circuit. The four-time Tradition winner shot his second straight 73 on Friday to enter the weekend at 2-over-par.
Defending champion Tom Kite is only slightly better. Hes at even par after back-to-back 72s.
Full-field scores from The Tradition