Final leaderboard (par=72):
-20 P Casey (Eng) -19 MA Jimenez (Spa), P Hanson (Swe) -18 S Gallacher (Sco) -17 R Karlsson (Swe) -16 SY Noh (Kor), J Edfors (Swe) Selected others: -14 D Clarke (NI) -13 M Manassero (Ita) -11 I Poulter (Eng) -10 S Garcia (Spa) -5 P Harrington (Ire)
Casey celebrates with caddie Christian Donald on the final green
Paul Casey won his first title for 20 months at the European Tour's Golf Champions tournament in Bahrain.
The Englishman parred his final hole for a 68 to finish on 20 under, having seen playing partner Peter Hanson (69) make bogey to drop back to 19 under.
Spain's Miguel Angel Jimenez carded a 67 to tie for second with the Swede.
Casey climbed to fifth in the world before Phil Mickelson later nudged him back to sixth with a second place in the PGA Tour event in California.
Mickelson moved back to fourth in the rankings behind world number one Lee Westwood, Martin Kaymer and Tiger Woods, with Graeme McDowell in fifth.
The US-based Casey, controversially left out of Europe's Ryder Cup side by captain Colin Montgomerie last year, sank a closing six-foot putt to clinch the title after 23 changes at the top of the leaderboard on the final day.
Casey came to the 429-yard last level with Hanson, but the Swede went from rough to sand before missing from 10 feet for a bogey five.
"It is one of the toughest battles I've ever had," said the 33-year-old Casey of his drought, which stretches back to May 2009 and his victory at the PGA Championship at Wentworth.
"It feels fantastic - the most important thing to me is winning and that was huge. The goal is obviously the majors, but how are you going to win major championships if you can't win regular events?"
Course-record rounds of 63 from Dane Soren Kjeldsen and England's Richard Finch proved deceptive in the desert because by the time the leaders came to the back nine a strong wind had picked up.
"We thought it was going to be benign, but we faced a course that was treacherous," said Casey.
Northern Ireland's Darren Clarke, Hanson's compatriot Johan Edfors and South African James Kingston all slipped up after holding at least a share of the lead. Clarke had bogey sixes on the ninth and 13th and finished with a double bogey.
Casey got his nose in front with an 18ft birdie putt on the 15th, but had his only bogey of the last two rounds on the next.
Jimenez's chances were alive again when he birdied the last and Hanson bogeyed it, but Casey got up and down from the rough by the green to squeeze home.
Scotland's Stephen Gallacher took fourth place and Swede Robert Karlsson, the defending champion in Qatar this coming week, came fifth.