That total for McCallister shatters the previous 54-hole record of 201, which Joe Daley set in 2002. Paul Gow also broke the 18-hole scoring mark as he capped a round of 10-under 61 with two birdies over his final seven holes Sunday morning.
McCallister, who is three strokes clear of Omar Uresti and four ahead of Bill Glasson, battled Uresti for the lead Saturday before play was halted due to heavy rain.
Uresti started the third round two strokes ahead of McCallister. He stretched that lead to three with a birdie at the first. However, momentum swung quickly in McCallister's favor. Uresti bogeyed the second and McCallister birdied the same hole to get within one shot of the lead.
McCallister birdied the third to forge a tie at minus-12. After pars at four and five by both players, Uresti reclaimed the lead with back-to-back birdies from the sixth. McCallister stayed within one stroke of the lead with a birdie of his own at the seventh, at which point play was halted due to heavy rain.
When the players returned to the course Sunday morning, McCallister and Uresti parred their first two holes to head to the back nine.
Things swung again in McCallister's favor. He birdied the 10th to tie for the lead and then birdied the 13th while Uresti bogeyed to complete a two-shot swing.
McCallister pushed his edge to three shots with a birdie at the par-4 16th. Both players then birdied 17 and parred 18 as McCallister held onto his three-shot advantage heading to the final round.
Gow, who survived right on the cut line of minus-2, leapt from a share of 56th place to solo fourth with his record round. He began his round on the back nine and scorched that side. He birdied his first three holes, before a par at the 13th halted his run.
After a birdie at No. 14, Gow parred the 15th. He capped a remarkable back side with three straight birdies to go out in 29. Gow made it four straight with a birdie at the first and later made back-to-back birdies from the fifth to get to 10-under for his round. He finished with three straight pars ending his chances of shooting a 59.
Gary Hallberg, the 2002 champion here, shot a 2-under 69 and shares 26th place at 6-under-par 207.