NEW YORK — Spinning in 70 mph second serves, grabbing at his hamstring during points, Andy Murray gritted his way through head-to-toe cramps to win at the U.S. Open. Murray outlasted Robin Haase 6-3, 7-6 (6), 1-6, 7-5 in the first round Monday during an afternoon that was hot but not particularly humid. He was mystified that the cramps came on so early — at the start of the third set after only about an hour and a half on court.