PEBBLE BEACH, Calif. -- Phil Mickelson put himself on the brink of a fifth victory in the AT&T Pebble Beach pro-am by turning a 3-shot deficit into a 3-shot lead when a wild day of weather kept him from finishing Sunday.

Mickelson was bogey-free with six birdies, and he made his big run starting with a 9-iron to a foot behind the cup on the par-4 ninth. That was start of a five-hole stretch when Mickelson made three birdies and Paul Casey had two bogeys.

About the only thing that didn't go Mickelson's way was the timing. The final round started an hour late because of rain, and then it was delayed two more hours when sunshine gave way to a hailstorm in a matter of minutes, covering the putting greens in a sheet of white. Mickelson was at 18-under par through 16 holes. Casey had a 3-foot par putt on the same hole when Mickelson tried to lobby for them to finish, even in the dark.

Phil Mickelson met with reporters in the twilight after play was halted Sunday at Pebble Beach. AP Photo/Eric Risberg

"I can see fine,'' Mickelson told a rules official. "I don't want to put Paul in a bad spot.''

Casey was at 15 under, tied with Scott Stallings, who closed with a 66. Along with an outside chance at forcing a playoff, finishing alone in second instead of a tie is a difference of $152,000, along with world ranking points and FedEx Cup points. Casey and FedEx executive Don Colleran had a 1-shot lead in the pro-am.

"I don't see how we can finish,'' Casey said as they walked up the 16th fairway. "We can't finish two holes in six minutes. I'd like to.''

Mickelson was standing on the 17th tee when he heard the horn sound to stop play, and he shook his head.

The rest of his day was far better than the weather. Mickelson is on the verge of winning for the 44th time in his career and matching Mark O'Meara with five victories at a tournament he first played in 1995. It also would be his first victory on American soil since the Phoenix Open six years ago. He won The Open that summer in Scotland, and the Mexico Championship last year.

His brilliant play still shared the stage with weather that was bizarre even by Pebble standards. Mickelson and Casey were waiting to tee off when clouds moved in quickly moved in, and rain turned into hail that pounded umbrellas, many of them held sideways to account for the wind. Greens quickly were covered by the tiny white pellets, and workers went from using squeegees for excess water to power blowers to remove the hail.

Sam Saunders, whose grandfather Arnold Palmer was among the Pebble Beach owners, scooped up hail and tossed it like a snowball. Patrick Reed's brother laid on his back and tried to make a snow angel. There was never a reasonable chance to finish in his pro-am format, with mostly foursomes across the golf course.

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Casey has never won in three previous times he had a 54-hole lead on the PGA Tour, all of them by 2 shots or more, and he was holding his own against the relentless pursuit of Mickelson, who missed three straight birdie putts from the 12-foot range by the slimmest margins. Casey had great par saves, and then Mickelson took off.

After his 9-iron into a foot at No. 9 to get within one shot, Mickelson holed a 12-foot birdie on the 10th with a drive that hugged the right side of the fairway and likely would have bounced into the ocean if not for conditions so soft from rain that balls plugged where they landed.

Casey blinked first with a bogey on the 11th hole, and another on the par-3 12th when his tee shot came up short and into the bunker. Mickelson poured it on, showing his skills have not deteriorated a bit at age 48, controlling spin beautifully to back pin positions. He just didn't want to stay another day.

"I get where Paul is coming from,'' Mickelson said. "We're going to have a good chance to come out on fresh greens. I have good vision, I can see fine and I wanted to continue. In all honesty, it's a good thing to play the last two holes in fresh conditions.''

Some players finished in the dark with no chance of winning, but showed the effect of playing without light. Scott Piercy had a 15-foot putt that was slightly uphill, and he still ran it 7 feet by the hole and three-putted for bogey. Jason Day closed with a 68 and was tied for fourth at 13-under 175 with Si Woo Kim (68).