The Englishman shot a sizzling six-under par 64 to hold the 54-hole lead with American Roland Thatcher on a 12-under total of 198.
Davis reaped seven birdies from the first eight holes to make the turn in 29 before finishing with just a birdie and a bogey over his final nine.
"It was just one of those days I came out hot," Davis told reporters. "Every club was the perfect club. I seemed to be hitting my shots in the right spot where I had an uphill putt."
That has been the story of the week for Davis, who has carved up the first nine holes and then held on coming in. He is 11-under on the front nine this week and just one-under over the final nine.
"When we hit the turn the wind picked up a little bit and played a little bit tricky for a few holes and then it dropped again," Davis said.
"So I was delighted to have hung in on the back nine."
Thatcher rolled in six birdies and a bogey in his 65, but dropped a shot on the 17th hole that cost him the outright lead, having taken top spot with three consecutive birdies from the 13th.
The leaders were two shots clear of Americans John Rollins (65) and James Driscoll (66), and Australian Stuart Appleby (67).
Defending champion Fredrik Jacobson of Sweden was among a group of six a shot further back, including triple major-winning Irishman Padraig Harrington (65) and American Matt Kuchar (66).
"I made eight birdies in 10 holes, which is nice when it's happening," Harrington said. "I have to carry that through to tomorrow and I have to go low again."
Play began early as much of the field were forced to finish their second rounds following storms on Friday.