FARMINGDALE, N.Y. — Ricky Barnes flashed a smile as big as his six-shot lead.

He was double digits under par, only the fourth player in U.S. Open history to get that low. He had a six-shot lead over his closest rival, while the stars struggled to make up ground. Phil Mickelson was making as many bogeys as birdies. Tiger Woods fell 15 shots behind.

It all changed in a New York minute.

When darkness settled over Bethpage Black as the final round was still young, Barnes was tied for the lead with Lucas Glover. Both of them were at 7-under par, five shots clear of anyone else. Neither has ever faced the nerves of contending in a major.

What once appeared to be a two-man race suddenly had endless possibilities:

— Mickelson made two long birdie putts on his last three holes for a 69 in the third round, and after pars on the two holes he played in the final round, he was only five shots behind.

— David Duval, a former British Open champion without a victory in eight years, kept coming back from sluggish starts and found himself very much in the hunt at 2 under with 16 holes to play.

— Woods finished a frustrating day on the greens with an eight-foot birdie putt on the 489-yard seventh hole, putting him at even par in the tournament for the first time since the 14th hole of the opening round. He was seven shots behind with 11 to play.

Barnes, who finished the third round of this rain-delayed U.S. Open with a one-shot lead at 8-under 202, chopped his way to bogey on the opening hole of the final round to lose his lead. Then he hooked his tee shot into gnarly clumps of the grass along a hillside left of the fairway on No. 2.

When the horn sounded to stop play, he quickly marked his position and walked briskly off the course.

‘‘It’s going to be pressure-packed tomorrow,’’ Glover said. ‘‘I’ll sleep fine. If not, I guess I’ll be tired.’’

Mickelson, determined to bring a fairy-tale finish to a U.S. Open career filled with disappointment, was on the third tee and had plenty of golf left.