Asked in a greenside interview what the performance did for his confidence, Mickelson said: "Absolutely nothing, because it's nothing like the course we'll see".
His path to victory these days is never going to be mundane, even in a tournament where he went an entire round without missing a fairway - a 20-year first.
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.
That was in 1998, when rain soaked the Monterey Peninsula in February, and the PGA Tour chose to play the third round the day after the PGA Championship ended up the Pacific coast at Sahalee. Mickelson's first goal is that fourth green jacket and he believes that even now, at the age of 48, he has the power and the putting touch to give McIlroy, Jordan Spieth and the rest a run for their money in eight weeks' time. There's really no carry-over other than I just really enjoy this place and seem to play some of my best golf here, that's probably about it. "But I wanted to try to finish tonight because I'm playing well". "So that led me to be pretty optimistic heading into this year".
"It's a lot more work and effort to play at this level, " Mickelson said.
Mickelson appears to be trending upward, as he also finished second at the Desert Classic in January.
Two players have won the Pro-Am and the U.S. Open at Pebble Beach in the same year: Jack Nicklaus and Tiger Woods. Bob Estes shot a 68 to finish third at 13 under, and David Toms was another stroke back after a 70.
Five-time major champion Mickelson will try to complete a career Grand Slam at Pebble Beach in June at the US Open, an event where he has finished second a record six times, most recently in 2013.
It would be wonderful for Phil to claim the career grand slam at Pebble with a second win there this season. The final threesomes of the day, with leader Paul Casey and his closest pursuer, Phil Mickelson, still had not teed off, bringing into question whether they'll be able to get 72 holes in before sundown on Sunday. "It's a totally different golf course".
Pebble, of course, would provide the ideal symmetry for such a storybook triumph.
"I really don't think there's any carry-over from here to the U.S. Open".
But the final day, and all week, was about the ageless Mickelson. All four players return to Pebble along with numerous game's best, including Jordan Spieth, Tony Finau and Jason Day.