By Mark Lamport-Stokes OAKMONT, Pennsylvania (Reuters) - Two months after winning his first major at the Masters, Danny Willett is having fun sizing up the prospect of becoming the first professional to complete a calendar grand slam of the four blue riband events. Tiger Woods came closest by holding all four majors at the same time after clinching the 2001 Masters, though his victories were spread across two years in what become known as the 'Tiger Slam'. Twelve months ago, Jordan Spieth raised hopes of becoming the first professional to complete the calendar slam with wins at the Masters and U.S. Open but fell short by finishing joint fourth at the British Open and second at the PGA Championship. More...