Casey closed with a 7-under 65 in the final round, his best score of the week, and beat Miguel Angel Jimenez and Peter Hanson by one shot for his eighth career European Tour win.
Last year's Order of Merit runner-up, Casey finished at 17-under-par 271 and won 257,877 euros to move into second place on this year's Order of Merit.
He was fully aware how tight things were at the top of the leaderboard.
'I did look at the leaderboards on the way around,' Casey admitted. 'I wanted to see what I needed to do. It's nice to look at them when you are playing good golf.'
Like Casey, Jimenez also stumbled to a late bogey -- but his was costly. Chasing the leader into the clubhouse, Jimenez hit a poor second shot and bogeyed the 17th at Abu Dhabi Golf Club, shooting a 68 to finish one back at 16-under 272.
'I had a very good chance of a playoff at least and maybe a victory, but I hit a bad shot at the 17th. I missed it, and there is no excuse,' Jimenez said. 'I am disappointed, but pleased with my game in general just three weeks into January.'
Hanson closed strong for a 68 and finished alongside Jimenez after posting back-to-back birdies at the 17th and 18th.
Last year's inaugural winner, Chris DiMarco, was a quiet fourth place. He closed with a 66 and ended two shots back at 15-under 273.
One shot further back, third-round leader and reigning Order of Merit winner Padraig Harrington settled for joint fifth place after shooting a 1-under 71.
'I suffered with my focus and bogeyed two holes on the back nine, which doesn't happen too often,' said Harrington, who bested Casey for last year's Order of Merit title on the final day.
'Such is the game,' he added. 'It's always disappointing when you have a chance, but I still feel I am well ahead of expectations for this time of year.'
Harrington was joined at 274 by Retief Goosen (68) and Jean-Francois Lucquin (68).
Henrik Stenson, last year's runner-up to DiMarco in the first Abu Dhabi Championship, finished in eighth place at 13-under 275 following a 67.