Play is split over the Stadium Course at PGA West and the Jack Nicklaus Tournament Course. Players rotate among the two courses through all six rounds as this marathon determines a golfer's fate for the 2007 season.
Anyone in the top-30 plus ties after Monday's final round will receive their PGA TOUR cards for next season. The next 50 will earn full privileges on the Nationwide Tour in 2007.
Australian Paul Gow posted a 4-under 68 on Thursday and is alone in second place at minus-6.
Steven Bowditch (68), George McNeill (66), Cameron Beckman (64) and Brian Bateman (65) are knotted in third place at 5-under-par 139.
Barcelo played the Nicklaus Tournament Course in Thursday's second round and parred his first three holes. He tallied birdies on both par-5s on the front side - at four and seven.
The 31-year-old Nevada resident flew out of the gate on the back nine. Barcelo birdied three in a row from the 10th, then picked up back-to-back birdies from the 14th.
He birdied the par-3 17th to post his 8-under-par 64 and grab the lead at Q-School.
Barcelo only played once on the PGA TOUR in 2006, a missed cut at the Chrysler Classic of Tucson. He teed it up eight times on the Nationwide Tour and only made half of the cuts.
Gow started on the back nine Thursday also at the Nicklaus Tournament Course and broke into red figures quickly with a birdie at the 11th. He added birdies at 13 and 14, but bogeyed No. 18.
The Australian record two straight birdies from the seventh to get into sole possession of second place.
Bob May, who lost to Tiger Woods in a playoff at the 2000 PGA Championship, shot a 7-under 65 and moved into a tie for seventh place with Steve Allan (71), John Mallinger (71), Bob Heintz (71) and Tom Johnson (68). The group finished at minus-4.
Overnight leader Scott Gutschewski struggled on Thursday. At the PGA West Stadium Course, he tallied two double-bogeys, three bogeys and three birdies for a 4-over 76. He is tied for 21st.
Two-time U.S. Open champion Lee Janzen carded an even-par 72 and is tied for 44th place at plus-1. Duffy Waldorf rebounded with a 4-under 68 and is tied for 21st at 1-under-par 143.