With a victory, he would match Mark O'Meara's record of five victories in the storied Pebble Beach event, which dates back to 1937 when it was won by Sam Snead. "I have pretty good vision, I'm playing well and I wanted to continue".
Even as Mickelson strongly hinted at wanting to finish - at point suggesting they play the 17th and he could scoot ahead to get a ball in play on the 18th so at least he could finish - Casey stood his ground.
Casey's consolation prize was teaming with Don Colleran to win the pro-am competition.
"It means a lot to me to play the final round as focused and as well as I did", said Mickelson, who started the final round three strokes behind Casey.
Mickelson's longest putt for par was 4 feet. "Paul's wonderful. He made me relax".
Casey has a four-foot putt to save par on the 16th green when play resumes at 8am (4pm GMT) on Monday, while Stallings holds the clubhouse lead on 15 under after a six-under 66. Mickelson was on the 17th tee, shaking his head when he heard the siren to stop play.
How it bodes for the rest of the year - particularly in June when the US Open returns to Pebble Beach - was of little concern to Mickelson.
Mickelson won on American soil for the first time since the Phoenix Open in 2013.
Mickelson finished at 19-under 268, while Englishman Paul Casey (71) birdied the final hole for second place on 16-under.
That also led him to enter this week's Genesis Open, which he had not planned to play, prior to defending a title at the WGC-Mexico Championship next week.
There was never a reasonable chance to finish in his pro-am format, with mostly foursomes across the golf course.
The late-morning hail quickly covered the greens and gave officials no choice but to suspend play, even before the leaders had teed off in northern California.
But the final day, and all week, was about the ageless Mickelson.
The four-time Pebble Beach victor nearly holed out from the ninth fairway to leave a tap-in birdie and complete a front-nine 33, before rolling in from 12 feet at the next to move into a share of the lead.
'Sometimes I get in my own bubble, ' Mickelson said. A frightful tee-shot was followed by a chip that failed to find the green and a third that wasn't much better and after a fast start, which had seen him birdie the first two holes and three of the first five, and following a run of 11 straight pars, the 38-year-old Aussie missed his bogey attempt and tapped in for a double-bogey five.
Jason Day closed with a 68 and was tied for fourth at 13-under 175 with Si Woo Kim (68).