Woodland received the advice from Mickelson on Tuesday, and quickly put it to good use, running in seven birdies for a six-under-par 64 in front of a gallery that included about 75 friends and family members at Bellerive.
"He (Mickelson) showed me on video what he thought I was doing wrong," Woodland said, explaining that he had put a new grip on his putter.
"It fixed everything. I didn't have to think anymore. I literally grab the putter and go, and it helps me release the club different. I've been releasing with my hands and this helps me release it more down the line, which has been huge."
Woodland is the fourth best driver on the PGA Tour this year using a metric that takes into account both distance and accuracy, but his chipping and putting have never matched his long game, hence his inability to post a top-10 in a major.
But he feels at home here in familiar surroundings not far from where he grew up in Topeka in the adjacent state of Kansas.
"I've been hitting the golf ball beautifully coming into this week, I have a million friends and family out here, which is pretty cool, so I was probably off pressing a little bit (early in the round)," he said.
"This is as close I'll ever play to home so it's nice to have the support.
"I snuck over here about a month ago and played and saw the golf course, and really enjoyed the layout. The turfs very familiar to me."
As for his major record, the 34-year-old knows it could be better.
"It's frustrating," he said. "I think 12th is the best I've ever finished, which is frustrating because I feel like where I am and where I should be (are different).
"The short game has really held me back. I hit the ball beautifully, but to contend week-in, week-out I have to get better in those areas.
"And it's been coming together. The putting was the last thing, because I've been hitting the ball very well.
"Now when I get out of position I have the short game to give myself a chance, and to see putts go in today was very, very cool."