Day and Nitties (69), both playing the TPC Stadium Course at PGA West, were at 15-under 201 through three rounds. The six-round tournament concludes Monday, with the top 25 and ties earning their cards for 2009.
Another player having a stellar third round was former 'Big Break' star Tommy 'Two Gloves' Gainey. He started the day in 102nd place and rocketed to 28th place by the end of the day.
He stands at 9 under, six off the pace.
Day, whose lone victory came at the MCI Heritage in 1999, ran off four birdies over the last six holes. Nitties made birdie on only one of the par-5s at the Stadium Course.
Geoffrey Sisk had a 69 on the Stadium Course and was two shots behind, while the group at 12-under 204 included Jay Williamson (69), Bryce Molder (69) and big-hitting Robert Garrigus (71).
Williamson made it through three rounds of the lucrative FedEx Cup playoffs this year, but failed to keep his card. The PGA Tour Q-School more closely resembles playoff pressure, a six-round event where only about 15 percent of the field will have full status on Tour next year.
In 12 years on tour, Williamsons best finish was losing in a playoff at the Travelers Championship last year.
Former PGA champion Mark Brooks had a 70 and was tied for 11th, although with four-time Tour winner Joe Durant (65) and Y.E. Yang of South Korea, who beat Tiger Woods in the HSBC Champions in China two years ago.
John Huston, a seven-time PGA Tour winner who opened with a 74, had a 65 on Friday to move into a tie for 31st.
Among former tour winners desperate for low scores was Frank Lickliter, last years medalist at Q-School who failed to break 70 for the third straight day and was tied for 119th.
There is no 72-hole hole at the qualifying tournament. Anyone finishing out of the top 25 will get either full or conditional status on the Nationwide Tour.