The 39-year-old hoped to make history with the 2012 title, after winning the competition at Gary Player Country Club in Sun City in 2010 and 2011.
But it was Germany’s Martin Kaymer who finished top of the select field of 12 players.
Westwood began with a one under par round of 71, with three birdies and two bogeys.
The second round saw him shoot a 73, his efforts spoiled somewhat by double bogeys at the fourth and 17th holes.
Four birdies on day three helped him to a round of 70 and in the final 18 holes he shot a 73, with four birdies, three bogeys and a double bogey at the par five 14th hole.
Westwood’s total of 287, one under par, was only good enough for fifth, as Kaymer finished first on eight under par.
The last tournament of 2012 for Westwood is Thailand Golf Championship at Amata Spring CC, in Bangkok this weekend.