Nick Flanagan, the reigning U.S. Amateur champion who hails from Australia, posted eight points in the final round to move into a tie for third place with 39 points. He was joined there by Thomas Levet (seven points) and Scott Gardiner (seven points).
Overnight leader Steve Webster struggled Sunday to minus-two points to fall into a tie for sixth with 37 points. He was joined there by Nick O'Hern, who notched three points.
Play was contested using the Modified Stableford Scoring system. The system awards eight points for a double-eagle, five points for an eagle and two points for a birdie. No points were handed out for pars, and one point was deducted for each bogey, with players losing three points for double-bogey or worse.
Davis dropped another point behind Webster as he bogeyed the first hole. He responded in fine fashion though. He rolled in a birdie try at the next and made it two straight as he birdied the third.
The Englishman was not done there. He drained another birdie try at the fourth and capped a string of four in a row with a birdie at the fifth.
Davis, who now owns two European Tour titles, fell back to 33 points as he dropped a shot at the par-4 seventh at Horizons Golf Resort. He atoned for the mistake with a birdie at the ninth.
He continued his surge on the back side with birdies on Nos. 11 and 13 to climb to 39 points, where he briefly held the lead. Davis again stumbled to a bogey at the 15th to fall out of the lead.
The 31-year-old bounced back with birdies at the 16th and 17th to grab a share of the lead at 42 points. Davis closed with a birdie at the last to move to 44 points, three clear of the field as Webster bogeyed the 13th and 14th to fall back to 41 points.
'I can't putt any better than that, that was unbelievable,' said Davis, whose other European tour title came at the 2000 Peugeot Open de Espana. 'I rolled the ball beautiful. I had three bogeys, but my main goal today was just to go out there and make as many birdies as I can and see where I finish.'
Webster's struggles continued, while Casey made an attempt at repeating as champion.
Casey opened the final round 10 points behind Webster. He got off to a quick start with back-to-back birdies from the second and picked up another birdie at the fifth.
He capped his opening side with a birdie at the ninth to move to 37 points. Casey again rolled home back-to-back birdies from the 12th to tie Webster atop the leaderboard.
Casey managed just one more birdie, at the 18th, to fall one point shy of becoming the first person to repeat as champion since Greg Norman won the first two ANZ Championships in 1988-89.
Webster struggled throughout his round. He bogeyed the second and third to quickly fall out of the lead. He vaulted back into the lead at 42 points thanks to an eagle at the par-5 ninth.
Around the turn, he dropped another shot at the 10th to fall into a share of the lead. Webster birdied the 12th to regain first, but fell out of the lead for good with bogeys at the 13th and 14th. He later bogeyed the 17th and double-bogeyed the last to fall into a share of sixth.
Ricky Barnes, the 2002 U.S. Amateur champion, shared eighth place at 35 points with Peter Fowler, Bradley Hughes and Brett Rumford.
Michael Campbell, a six-time winner on the European Tour. was one point farther back with 34. He was joined there by Joakim Haeggman, Jose Manuel Lara, Martin Lemesurier and David McKenzie