Tiger Woods, back as world number one this week, could lose it to Vijay Singh again at the US Open.
The Fijian has to finish in the first four to have a chance. If he wins Woods would have to be second to remain top, if he is second Woods has to be fifth, if he is third Woods has to be 16th and if he is fourth Woods needs to be 52nd.
If Singh is tied fourth Woods would have to miss the cut to lose his top spot.