Bryant collected his first major championship win and fourth Champions Tour crown as he finished at 6-under-par 282.
'Dreams do come true. Thirty-five years ago standing on a practice putting green I dreamed about hitting that putt and winning the U.S. Open as a kid,' admitted Bryant, who collected $470,000 for the win. 'Miracles happen.'
Watson got to 9 under with a birdie on the par-4 10th, but dropped six strokes over the next five holes. Watson posted a 7-over 43 on the back nine en route to a 6-over 78 at Whistling Straits that left him alone in fourth at 1-under-par 287
'I hit the ball in the rough too many times, and I got my just reward hitting the ball in the rough,' stated Watson. 'I had to put the ball in the fairway and I didn't do it enough times, that was the killer for me.'
Ben Crenshaw, who hasn't won since the 1995 Masters, carded a 2-under 70 to end alone in second place at 3-under-par 285. Roberts was one shot back at minus-2 after closing with a 2-over 74.
Watson opened with a birdie at the first and was four strokes clear of the field.
He dropped a shot on the fourth, but consecutive birdies from the ninth got him to 9 under, three strokes clear of Bryant, who was playing three groups ahead of Watson.
The big swing came at the par-5 11th. Bryant played his third to two feet and kicked that in for birdie to move to 7 under.
Watson, the 1982 U.S. Open champion, found a fairway bunker of the tee and played down the fairway with his second. He came up short in the rough with his third, then chipped his fourth short off the putting surface.
He pitched his fifth within 5 feet, but two-putted for double-bogey to slip to minus-7. Watson still led by one as Bryant could not save par from a greenside bunker on the 12th.
Watson's slide continued with a three-putt bogey on 12 and a two-putt bogey from 5 feet at 13 dropped him to 5 under and into a share of the lead with Bryant, who got to that number when he could not save par from a bunker at 14.
'When I made double-bogey at 11, a reachable par-5, that was a real wake-up call right there that the golf course wasn't going to give in very easily,' Watson said. 'Bogeys on the next two holes, a lousy three-putt at 12 and not getting the ball up-and-down from the back at 13 was kind of a harbinger for the rest of the day.'
Bryant moved one stroke ahead of Watson with a two-foot birdie putt on the par-5 16th. Watson continued to struggle as he double-bogeyed the 15th.
Bryant, who led the field in greens in regulation this week, knocked his tee shot to 6 feet at the 17th. He missed the birdie try, but tapped in for par. At the 18th, Bryant two-putted from about 30 feet to close out the win.
'I hit the ball solidly all week, which in the wind is good,' said Bryant, who hit 30 of 36 greens in regulation in the final two rounds. 'I got the ball close to the hole starting out today. The front nine I think I had six good birdie putts and made four of them, that got me more focused.'
Crenshaw got within two of the lead thanks to birdies on nine, 11 and 13. At that point, he was 4 under. However, he wrapped bogeys at 15 and 17 around a birdie on 16 to get end at 3 under.
'We had a heck of a test of golf this week,' said Crenshaw. 'I played well for the most part today, but had a little bobble at the finish. I just didn't play quite well enough.'
Jay Haas, the reigning Champions Tour player of the year, closed with an even- par 72. He ended in a tie for fifth at 1-over-par 289 and was joined there by Sam Torrance, Denis Watson, Tom Purtzer, D.A. Weibring and Joe Ozaki.
Jim Woodward, Lonnie Nielsen, Vicente Fernandez, Larry Nelson and Mark O'Meara were one stroke further back at plus-2.