Starting the day one stroke behind overnight leaders Ryan Grant and Ryan Carter, Walker calmly went out and carded a 6-under 66 at Green River GC to give himself some breathing room with one day to go.
Walker has a three-day aggregate of 14-under 202.
Scott McNeil of Calgary posted a 7-under 65 to move into a tie for second spot with Californian John Lieber at minus-10. McNeil, who played his rookie season on the Canadian Tour last year, moved up from 18th and will play in the final threesome Friday.
Green River and Los Serranos CC are playing host to Qualifying School this week. Those who played Green River Thursday will move to Los Serranos for the final round.
Chris Botsford is in fourth spot, five shots back. Grant, Carter and Benjamin Greve are at minus-8.
A total of 155 players representing 11 countries are in California looking for Tour playing privileges. Friday marks the final chance for competitors to secure one of the 20 exempt or 10 non-exempt cards to be handed out.
Adam Speirs of Winnipeg is on the bubble for a card, holding down a share of 28th at 3-under 213. Julien Trudeau of Montreal is one of nine players at 2-under.
The Canadian Tour begins its 2006 season with a two-event swing through Austin, Tex. starting with the Yes! Golf Barton Creek Classic March 2-5.