Ernie Els will take on Tiger Woods at Royal Troon this week not only for the Open title they both cherish, but also for the world No 1 spot.

If Els can repeat his triumph of Muirfield two years ago then Woods, winner at St Andrews in 2000, will have to be 17th or better to stay top of the rankings.

Vijay Singh, though, is too far behind - just - to have the same added incentive as Els.

Singh needed to be in a two-way tie for fourth place at the John Deere Classic in Illinois on Sunday to move within striking distance of the American. He finished in a four-way tie for fourth.

Woods has been No 1 on and off since June 1997 and continuously since August 1999. And if he is there for another month he will have headed the rankings for longer than anybody else since they were introduced in 1986.

But there is not the same certainty about that any more. Woods has undoubtedly lost his aura of invincibility.

Having won seven of the previous 11 majors Woods has not won one for over two years. And, perhaps even more worringly for him, he has not won any stroke play event since last October.

The gap has been narrowing as his drives have been widening. The 28-year-old ranks an astonishing 155th in accuracy on the US Tour this season and nobody's swing has come under closer scrutiny.

Woods was out working on it at the crack of dawn yesterday. He teed off with close friend and 1998 winner Mark O'Meara at 6.30am and had completed the 18 holes before most of the crowd had arrived.

Els, on the other hand, was more low-key, resting up a bit following his third place finish in the Scottish Open at Loch Lomond.

Troon is where the South African made his Open debut as a 19-year-old amateur in 1989. It is also where Woods had the lowest round of his major championship career, a 64 in the third round seven years ago.

That, though, was his only sub-par round of the week and Woods, three months after winning the Masters (his first major as a pro) by a record 12 strokes and with a record 18 under par score, finished a disappointing 24th.

''If the prevailing wind is blowing, it's a perfect links course,'' he said. ''Every hazard is right in front of you. The pot bunkers are very penal and you just have the hit the ball well.

''I remember that it seemed like everybody was two, three or four under par on the outward nine and almost everybody backed up on the inward nine.

''There are some tough holes coming in, especially the 490-yard par four 11th, 431-yard 12th and 472-yard 13th. That's a brutal stretch and will separate a lot of players.

''I also remember how difficult the 222-yard 17th is and how tough it is to hit the fairway at the 457-yard 18th. It seems like there are bunkers everywhere and they are almost impossible to miss.''

Woods has already watched some videos from 1997 so he could visualise the holes before flying in.

''I know there have been several changes to the course since then, but it never hurts to get a mental picture of a course before you play it.

''As always, the keys to playing well on a links course are patience, ball-striking and imagination. Without all three, you have no chance to win.

''Probably the biggest key is you have to understand you're going to get some really bad bounces. You just have to accept that and be prepared for crazy kicks.

''More so than any tournament, you have to be able to control your ball flight. We don't play enough tournaments where you play the ball along the ground.''

Lee Westwood has chosen to be ''reclusive'' in the build-up.

The former European No 1 has been paired with Tiger Woods in the opening two rounds on Thursday and Friday.

The pair will tee off along with Greg Norman at 1.42pm in the first round and at 8.31am the following morning.

''We've had Henmania and that's enough,'' said Westwood on his wish to stay out of spotlight.

''Just keep it low-key, stay out of the way and not get caught up in the hype. It's probably the one time you shouldn't do any interviews, but people who don't cover golf week-in week-out suddenly turn up and want a piece of you.

''This year I'm not doing any and going into it fresh.''