Three shots behind when he stood on the 15th tee, Lowery made up quick ground when Singh made three consecutive bogeys, then won on the first hole of a sudden-death playoff with a 7-foot birdie. At 47, he became the oldest winner in the 71-year history of the AT&T Pebble Beach National Pro-Am.
Lowery closed with 4-under 68 and won for the third time in his career, all in playoffs.
Singh recovered from his three bogeys with a wedge that stopped 2 feet away for birdie on the final hole for 71 to force the playoff. Both players finished at 10-under-par 278.
But the Fijian's troubles only got worse playing the famous 18th hole at Pebble Beach a second time. His drive found a bunker to the right, and his second shot clipped the top of the bunker, leaving him 192 yards short of the green. A 4-iron for his third shot plugged into the side of another bunker, and he did well to blast out to 8 feet and make par.
Lowery's birdie putt was good all the way, an amazing victory for a variety of reasons, least of all Singh's collapse.
Lowery was No. 305 in the world when he arrived on the Monterey Peninsula. He finished 148th on the money list last year because of a wrist injury, and was given eight tournaments to make $282,558 to keep his card for the rest of the year.
That's no longer a problem.
Lowery earned $1.08 million and a two-year exemption, sending Singh home to question whether his retooled swing can hold up under pressure.
The first playoff at Pebble Beach since 1992 didn't seem remotely possibly when Lowery walked off the 14th green with a bogey. He was three shots behind Singh, who had just hit a brilliant flop shot to 6 feet to save par on the 13th.
Singh went at the flag on the 14th with a sand wedge from 92 yards, but it was a tad strong and spun down the slope, and the best he could do was chip to 20 feet and make bogey. He missed the 15th green to the left, chipped weakly and missed an 8-footer for par.
His fairway metal found a bunker off the 16th tee, and Singh powered that shot over the green, down the slope and into the back bunker. He blasted through the green and two-putted for bogey from the fringe to fall into a tie. Singh arrived on the 17th tee in time to watch Lowery hole a 20-foot birdie putt to take the lead.
Singh's 3-foot par putt on the 17th swirled around the inside of the cup before falling, and his tee shot on the 18th was headed for a tree until it bounced off the trunk and deflected to the right. That gave him a clear shot at the green, setting up his wedge to 2 feet.
Dudley Hart, who started the final round tied with Singh, didn't make a birdie until making three in a row at the end for a 72 to finish one shot out of the playoff. He tied for third with John Mallinger (65) and Corey Pavin (66). Jason Day, the 20-year-old from Australia, finished alone in sixth after shooting 70.
Pebble Beach was the final tournament to qualify for the Accenture Match Play Championship. Pat Perez shot 72 and tied for 24th, but it was enough for him to get into his first World Golf Championship. Perez moved up two spots to No. 64, and with Ernie Els not playing, he will face Phil Mickelson in the first round. J.B. Holmes, who missed the cut at Pebble, dropped to No. 65 and gets Tiger Woods, provided no one else withdraws.