SAN DIEGO, Calif., June 20 (Reuters) - Spaniard Jon Rahm birdied the final two holes to emerge last man standing and win a wild U.S. Open at Torrey Pines on Sunday. The only serious contender to avoid a bogey over the last nine holes, Rahm shot 67 and finished at six-under-par 278, one stroke in front of South African Louis Oosthuizen, whose birdie at the final hole was not enough to force a playoff.