Nedbank Golf Challenge final leaderboard: -17 L Westwood (Eng)
-9 T Clark (SA) -8 R Goosen (SA) MA Jimenez (Sp) -5 E Els (SA), R Fisher (Eng) -3 P Harrington (Ire), R Allenby (Aus)
Westwood reached the top of the world rankings in October
World number one Lee Westwood stormed to an eight-shot victory in the Nedbank Golf Challenge in South Africa.
The Englishman chipped in for a birdie on the 18th to clinch a final-round 68 and finish 17 under par, with Tim Clark of South Africa a distant second.
As his rivals struggled in swirling winds, Westwood carded five birdies to win the $1.25m (£792,000) first prize.
South African Retief Goosen shot a 68 to end up eight under and share third with Spain's Miguel Angel Jimenez.
Westwood's stunning chip from well off the 18th green at the Gary Player Country Club rolled gently into the hole to provide a fitting finale to a week in which he showed exactly why he is now rated the best golfer on the planet.
"I think that's the first time I've chipped in all year," he said. "It's what you call a grandstand finish. It was a good time to do it."
"I've been playing here for 15 years and it's something I've always wanted to win. The finish was tough and I was just pleased to get it done in the end."
Westwood went into his last event of the season knowing he could lose top spot to Tiger Woods, whom he dethroned at the end of October, if he failed to finish in the top two and the American won the Chevron World Challenge in California.
In the event, Westwood did not allow Woods a look-in, firing a four-under-par 68 in the opening round and a 64 on Friday to take a commanding lead.
He consolidated that with a more modest 71 in tricky scoring conditions on Saturday but was back to his best in Sunday's finale.
Two birdies on the front nine took him seven shots clear of the field and he picked up further strokes at the 10th and 13th.
A dropped shot at 17 was a rare blemish on the scorecard but he made up for that on the last hole with a stunning chip after dragging his second shot left of the putting surface.
Attention then turned to Westwood's playing partner Clark, who holed a tricky eight-footer to cling on to second place ahead of two-time US Open champion Goosen, who produced his best round of the week with a 68.
England's Ross Fisher, joint second overnight on eight under, got off to the worst possible start with bogeys on the first two holes, eventually posting a three-over-par 75 for a share of fifth place.
Padraig Harrington, Ireland's three-time major champion, also struggled to a 75 on the final day to end up three under, one better than Englishman Justin Rose.