Andalucia Masters final leaderboard:
-3 G McDowell (NI) -1 S Kjeldsen (Den), D McGrane (Ire), G Maybin (NI) Selected others:+7 M Kaymer (Ger)
Westwood is the first European since Nick Faldo to be world number one
England's Lee Westwood has become world number one for the first time, ending American Tiger Woods's 281-week reign at the top of the golf rankings.
German Martin Kaymer needed a top-two finish at Valderrama to become number one himself but ended Sunday's fourth round well off the lead at seven over.
Kaymer fired a final-round 75 to finish 10 shots behind winner Graeme McDowell.
Westwood, 37, becomes Europe's first number one golfer since compatriot Nick Faldo achieved the feat in 1994.
A calf problem has ruled Westwood out of action for the last three weeks but, despite not being able to influence Sunday's result in Spain, he was clearly delighted by his accomplishment.
Lee deserves it. He's one of the greatest guys on the European Tour
Asked if it was the most satisfying moment in his career, Westwood said: "Yes, I think so. It's a dream everyone has to say there is nobody better than me at the moment. You have to say it's a highlight. It's a great honour and a big responsibility."
And Westwood is confident his latest career milestone is evidence he is on his way to ending the wait for a first major championship title.
"Becoming number one is confirmation that I'm working on the right things more than anything," he said. "This is nothing but a positive thing.
"Winning majors is something you learn to do. You get into position as often as possible and try not to make the same mistakes again. I have seen most things by now and hopefully I will know what to do."
Kaymer, the USPGA champion, had started the day nine shots adrift of leader Graeme McDowell in Spain after opening with a 72 on Thursday and following that with a 75 and a third-round 70.
Most weeks at world number one
Tiger Woods (USA) 623 weeks
Greg Norman (AUS) 331 weeks
Nick Faldo (ENG) 98 weeks
Seve Ballesteros (ESP) 61 weeks
Ian Woosnam (WAL) 50 weeks
Nick Price (ZIM) 44 weeks
Vijay Singh (FIJ) 32 weeks
Fred Couples (USA) 16 weeks
David Duval (USA) 15 weeks
Ernie Els (SA) 9 weeks
Bernhard Langer (GER) 3 weeks
Tom Lehman (USA) 1 week
The 25-year-old German therefore required a sensational effort on Sunday to move up the leaderboard and claim top spot, but despite a birdie on the third he showed little of his recent fine form and ended the day four over par.
"Of course I'm disappointed," said Kaymer. "I thought if I had a fast weekend I could still play a role but I missed too many putts. You have to accept it isn't your week. I don't think trying to get to number one played any part.
"It was in the back of my mind but I didn't play differently, any more aggressively or defensively. I liked the challenge and I think I'll have another chance in the next few weeks.
"Lee deserves it, he's one of the greatest guys on the European Tour."
McDowell's victory sees him close the gap on Kaymer in the Race To Dubai, the European Tour's money list. The Northern Irishman also moves up to 10th in the world rankings, becoming the sixth European in the top 10 alongside four Americans.
For 14-time major champion Woods it is a remarkable fall from grace, having at one time seemed unstoppable in his assault on Jack Nicklaus's record of 18 major wins.
He has faltered badly after a knee injury and revelations about his personal life that saw him take an extended break from the game.
Westwood intends to return at next week's WGC-HSBC Champions event in Shanghai, where he will face Woods as well as Kaymer and Phil Mickelson.
"I have a great relationship with Tiger," added Westwood. "We have mutual respect and have always got on well, on and off the course. I give him a little bit of stick and he gives me a little.
"When Tiger was in his pomp everyone thought it [the number one spot] was unattainable. But form comes and goes - I'm a perfect example of that - and when we started to get a bit nearer the top of the rankings we started to think it was obtainable."
Westwood's career trajectory has been through two phases.
He spent 180 weeks in the top 10 between 1998 and 2001, winning the Order of Merit in 2000 and reaching world number four, but took a break from the game after the birth of his first child and rather lost his way, dropping outside the top 250 in the rankings.
His next victory was not until the BMW International Open in 2003, but when he won the Andalucia Open and British Masters in 2007 he moved back into the top 50 and by the end of the 2008 season he was back in the top 10.
The Worksop golfer won the inaugural Race To Dubai in 2009, when he was
one shot away from being in a play-off for the Open Championship
with Tom Watson and Stewart Cink.
At this year's Masters he was one stroke ahead going into the final day but was
denied by Mickelson's magnificent final round of 67,
and he was
runner-up to Louis Oosthuizen, seven shots adrift, at the Open at St Andrews
before the calf injury hampered the remainder of his season.
Westwood turned professional in 1993 after becoming British youths champion and has won 20 times on the European Tour and twice on the USPGA Tour, with four triumphs on the Japan Tour and six in other tour events.
The father of two has made seven Ryder Cup appearances, featuring in the winning side five times including
the most recent success at Celtic Manor in September.
Lee Westwood holes 30-foot putt at Ryder Cup (UK users only)