He played two holes just as well as the previous 16 and polished off his bogey-free final round with one last birdie for a 7-under-par 65 and a three-shot victory over Paul Casey in the AT&T Pebble Beach Pro-Am.
The last two groups didn't tee off until after two weather delays, with rain postponing the start of play for an hour and a hailstorm bringing another two-hour hold-up.
Nobody has ever won a major championship at the age Mickelson is at now, but then again, not too many players have had the confidence to play two holes essentially blindfolded - as he wanted to do to finish this off Sunday night instead of Monday morning.
"As much as I would like to finish, it's probably a good thing", Mickelson said. The 48-year-old Mickelson said, "I have pretty good vision".
Casey made a decision to stop ahead of his putt on 16 on Sunday, even as Mickelson pushed to start the par-3 17th hole.
Also the tournament victor in 2010, Langer moved within six of Irwin's tour victory record and won in his 13th straight season to extend his record. Casey has a 3-foot par putt to stay three shots behind when they return at 8 a.m. Monday to play the par-3 17th and the par-5 18th.
Mickelson's first Pebble Beach title back in 1998 came when the weather was so bad that the final round was actually played on a Monday in August - six months after the tournament began.
"It's been a treat this week", said Casey, who had entered this week with two weeks of rest after a tie for second at the Singapore Open on the Japan Tour. "I just get in my own little bubble and I don't see the big picture".
"(It means) absolutely nothing because it's nothing like the course we'll see", Mickelson said.
Phil Mickelson has won the weather-affected AT&T Pebble Beach Pro Am and [1000.0] shot, David Law, has won the ISPS Handa Vic Open.
Mickelson finished at 19-under 268, while Englishman Paul Casey (71) birdied the final hole for second place on 16-under. Before he won, he marked his 500th PGA Tour cut made on Friday.
His brilliant play still shared the stage with weather that was weird even by Pebble standards.
On Monday morning, he had a change of heart and said he thanked Casey for standing his ground.
Casey was pleased to join Colleran as a Pro-Am champion after a near miss previous year. Scott Stallings moved up 80 spots to No. 150 after finishing alone in third, while T-4 results pushed Jason Day from 12th to 11th and Si Woo Kim from 70th to 62nd.