"He played great today, and this was special", said Streelman, who finished sixth among the pros and four shots back of victor Ted Potter Jr.
Potter, who won just over $207,000 (£150,000) past year, picked up more than $1m for his victory on Sunday.
"Just back from my mini-tour days, tournaments I've won in the past, just drawing back from past experience of winning golf tournaments", he said.
The victory was a remarkable comeback by Potter, who incurred a fractured right ankle in a "freak accident" in 2014 when he slipped on a path.
Mickelson birdied three of his final five holes to get to 14 under, with Johnson nudging in from three feet at the 18th and Day recovering from finding the beach at the par-five last to save par and also finish three off the pace.
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American Kevin Streelman (68) finished alone in sixth and Scott Stallings (66) was seventh at 12-under 275, five shots adrift of Potter.
The left-hander played on the Web.com Tour previous year to regain his PGA Tour card after time out with a broken ankle. But it was on the front nine that he really sizzled, playing the first seven holes in seven-under par with five birdies and an eagle. After kicking off in 67-72-66, the ASU product began in solo 8th, four shy of co-leaders Potter, Jr., and Dustin Johnson. That included a birdie chip from the rough on the par-three seventh hole. Despite the disappointing finish this week, Johnson, the world number one, has already racked up three top-two finishes this season.
Potter finished at 17-under 270 for his second PGA Tour win, after his previous success in 2012.
"I gave it a shot on the back nine", he said. Despite his stellar play in his last two tournaments, Day won't travel for this week's Genesis Open.