Garcia knocked Khan down three times with the end coming at 2:28 of the fourth round when referee Kenny Bayless stopped the bout.
Garcia, who already had the WBC title, now has 24 wins and no losses. He kept his perfect record intact by surviving the early rounds before using a perfectly-timed left hook late in the third round that caught Khan flush on the ear.
Khan, of Great Britain, suffered just the third loss of his career.
He never recovered fully from that third-round knockdown. Khan got up from the first knockdown only to be knocked down twice more in the fourth round which had turned into a slugfest with the fighters trading heavy shots in the centre of the ring. AGENCIES