World matchplay champion Els did not ease up even though the pair carried a 13-stroke advantage into the final round.
He closed with a 67 to finish 16-under and also carried off the International Trophy as leading individual. Westner finished three back in second place after a 70.
The low round of the tournament and final day was claimed by Ireland's Darren Clarke who shot a 64 despite a double-bogey six at the 10th hole.
The South African duo shared the $400,000 (pounds 250,000) first prize with Els collecting an additional $100,000 (pounds 62,500) for his individual success.
Scotland were unable to hold off the challenge of the United States, finishing third on 10-under as Tom Lehman and Steve Jones improved by five shots on the final day to finish on 11-under.
Greg Norman produced a flawless final round of 69 to take the Australian Open in Sydney for the fifth time. The Great White Shark had an eight- under-par total of 280, with Wayne Grady, the 1990 US PGA champion, second after a three-under-par 69. New Zealander David Smail had a 73 to finish third on 290. Tiger Woods, who came close to missing the cut after an opening round of 79, completed his recovery with a top 10 finish.
The former PGA champion and Ryder Cup player Paul Way's 75 for 18 over at the Sotogrande Tour Qualifying School means he will enter next season without a Tour card for the first time since he turned professional in 1981.Reuse content