* Spieth wins after Johnson misses four-foot birdie putt
* Is sixth player to win year's first two majors in same season
* McIlroy signs off with 66 (Updates after end of final round)
By Mark Lamport-Stokes
UNIVERSITY PLACE, Washington, June 21 (Reuters) - Masters champion Jordan Spieth added another chapter to golf's record books with a nerve-jangling victory by one shot at the U.S. Open on Sunday after a wildly fluctuating final round of high drama.
The American young gun sank a curling 28-footer to birdie the 16th and forge three ahead, then shrugged off a double-bogey at the 17th before becoming just the sixth player to slip into a green jacket and hoist the U.