Play was suspended due to the threat of lightning at 1:50 p.m. ET (1750 GMT), 10 minutes before overnight leader Johnson Wagner was scheduled to tee off at The Greenbrier's Old White Course in pursuit of his fourth victory on the PGA Tour.
Though the final round eventually resumed at 5:00 p.m. ET, there was very little chance the lead groups would be able to finish the tournament on Sunday with sunset expected at 8:45 p.m. ET.
"With this cloud cover, I think we can play until about 8.30 p.m.," Slugger White, the PGA Tour's vice president of rules and competition, told CBS Sports.
On Saturday, the lead groups completed the third round in three hours 45 minutes. Final rounds generally take longer with players having to cope with the mounting pressure of a title on the line.
American Wagner, who fired a sparkling six-under-par 64 on Saturday to seize a two-shot lead after the third round, was prepared for all eventualities.
"Rain, sun, shine - it doesn't really matter," Wagner, 33, told CBS Sports. "I'm ready to play if it's tomorrow or Tuesday. I am just happy to be in this position."
Wagner, who won his most recent PGA Tour title at last year's Sony Open in Hawaii, will start the final round with a 14-under total of 196.
Fellow American Jimmy Walker, seeking his first victory on the U.S. circuit, was alone in second with Swede Jonas Blixt a further two strokes back at 10 under.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Gene Cherry)