David Howell, who was one of four first-round leaders with Davis, shot an even-par 72. Howell stands at 3-under-par 141 and shares second place with Thomas Bjorn (68) and Soren Hansen (71). Bjorn's 68 was the low round of the day in Friday's windy conditions.
Michael Campbell carded a 2-under 70 on Friday. He was joined in a tie for fifth place at minus-1 by Steve Webster, who shot 71.
Davis began his round on the back nine of the Arden Course at the Marriott Forest of Arden Hotel & Country Club. He converted a birdie try at the 11th, his second, and came right back with a birdie on 12 to get to 5 under.
The 30-year-old tripped to a bogey at No. 16 when he missed a 2-foot par putt. Davis had more problems at the par-5 17th. He hit into water twice on the hole and walked away with a triple bogey.
Davis rebounded around the turn with a birdie on the par-4 first. The 2004 ANZ Championship winner carded his fourth birdie of the day on the third, his 12th.
The Englishman got back to minus-4 thanks to a 20-foot birdie putt on the par-3 fifth. However, Davis faltered to his second bogey in two days at the sixth. He bounced right back with a birdie on the seventh to claim the outright lead.
'I have always driven myself into the ground and as much as I am focused on my golf right now, I am focusing somewhere else,' Davis said. 'I am really enjoying spending time with my wife and son and we have another on the way at the end of the year. I am enjoying that side of things and it is helping me on the golf course.'
Bjorn also began on the 10th tee in the second round. He slipped to a bogey at the par-4 11th to drop back to plus-2 overall. The Dane rebounded with a birdie on 13 and got to even-par with his second birdie in two days on the par-5 17th.
The 34-year-old poured in back-to-back birdies putts from the third to move to minus-2. Bjorn got within one shot of the lead with a birdie on the par-5 seventh. He parred in to share second place.
'I think I screwed the right head on this morning,' said Bjorn. 'It was never going to be the prettiest of golf in these conditions, but I felt I kept the momentum all the way and did all the right things. It was a case of trying to eliminate mistakes all day and I succeeded very much in that.'
Hansen opened with a bogey on No. 10. He bounced back with an eagle on the 12th to get to 3 under. The 2002 Irish Open winner bogeyed the 14th, but was able to make the turn at 3 under after a birdie on 17.
On the front side, Hansen tripped to bogeys at one and five. However, he did manage a birdie in between on the third. Hansen birdied the seventh for the second straight round to end at minus-3.
Howell played the back side first and posted two birdies and two bogeys on his opening nine. On the front side, the Englishman birdied the first. However, Howell struggled to back-to-back bogies from the second to drop back to 2 under.
The 29-year-old came back with a birdie on the fifth. Howell bogeyed the sixth, but was able to get within one of the lead with a birdie on seven.
Simon Dyson and Peter Baker share seventh place at even-par 144. Angel Cabrera, Scott Drummond, Richard Finch, Marcus Fraser, Oliver Wilson, Ian Woosnam, Richard Green and Patrik Sjoland are one stroke further back at plus-1.
David Lynn, who also shared the first-round lead, struggled to a 5-over 77. He stands at 2-over-par 146 alongside defending champion Barry Lane among others.
Ben Mason, the final first-round co-leader, stumbled to a 12-over 84 and missed the cut at plus-9. The cut line fell at 7-over-par 151 with 77 players moving on to the weekend.