JAKARTA (Reuters) - Lee Westwood celebrated his 38th birthday with a comfortable three-stroke victory at the Indonesian Masters on Sunday to stay in the hunt for regaining the world number one spot from German Martin Kaymer. The world number two will top the rankings if fellow Briton Luke Donald, who leads by a stroke at the $750,000 Heritage tournament in South Carolina after the penultimate round, fails to land the trophy. Donald could overtake Kaymer, who is not playing this week, and Westwood, despite his victory, because the Heritage carries more ranking points than the Asian Tour event. Westwood, who led by five strokes after the third round, but dropped a shot on the second to make the turn at even-par 36 at the Royale Jakarta Golf Club.