Day, the 2015 PGA Championship victor, held off Americans Aaron Wise and Nick Watney with a final-round two-under par 69 to finish 72 holes on 12-under 272 for a two-stroke victory at Quail Hollow in Charlotte, North Carolina.
And as well as those star players performed, they couldn't match Peter Uihlein, who shot 62 after a six-hole stretch that included five birdies and an eagle.
"I would probably prefer more of the PGA setup", said Fowler, who tied for fifth at the '17 PGA but also has three top-10 finishes at the Wells Fargo including a victory in 2012. "I'm super, super excited", Watney said.
If you've felt that it's taken a while for this Wells Fargo Championship to find its plot, at least from a competitive standpoint, you're not alone.
PGA Tour rookie Aaron Wise almost had a collapse late until he salvaged a most unlikely bogey.
Mickelson had his lowest round of the season as a seven-under 64 elevated him up the leaderboard to five under and in sole possession of 10th spot, while Woods solved some of his putting problems with a three-under 68, which left him on one under. Nick Watney had a 66 and was two behind.
"I was so close to shooting about 7 under on that back nine, " Woods said after shooting 34 on the closing nine holes. Woods saved par by making a 14-footer on 14, but he made his third bogey of the day on 15 when he three-putted from 18 feet.
Tiger Woods said he's on the verge of putting it all together and winning his first PGA tournament in five years - if he can just start rolling the ball a little better on the greens. "Then hit a putt hard off again on the second putt, and the grain just ate it up". Peter Uihlein took advantage of Quail Hollow early with a 9-under 62. He starts Sunday four shots out of the lead.
"I just stayed in my lane, " Day said.
Woods picked up six birdies to reach one-under 212 but finished the round on a sour note with a three-putt bogey on 18.
Park, last year's U.S. Women's Open champion and the top-ranked player in the field at No. 5, had seven birdies and one bogey at the 6,475-yard Old American Golf Club, which is hosting the event for the first time. The previous player to win on the same course where he won a major the previous year was Jack Nicklaus in the 1973 Bing Crosby National Pro-am at Pebble Beach.
If Woods had putted well this week, he could've approached contention. So I've got to get up every morning and do everything I possibly can to get back to that ultimate goal of getting back to No. 1.
Greg Chalmers is in 25th position while Adam Scott made the 36 hole cut but was not able to advance to Sunday play after his round of 72 left him amongst those restricted due to field size numbers.