The victory also makes Henderson the No. 2 woman golfer in the world. That is her nature: she goes for it. But it seemed like it had all sunk in in a hurry.
Like Henderson, Post also won her first major in a playoff, downing Kathy Whitworth by seven strokes in 1968 to become the first non-U.S. player and rookie to win the LPGA championship.
"I had so much fun out there on the back nine, and even the front nine yesterday", Henderson said.
SAMMAMISH, Wash. - Brooke Henderson beat top-ranked Lydia Ko with a birdie on the first hole of a playoff in the Women's PGA Championship after overcoming a three-shot deficit on the back nine. "And even just down the playoff hole, for her to go that Tiger line, just right of the left trees, going right for the pin and to have the flawless yardage, she just played great". Later, she would hoist the big silver PGA championship trophy over her head like it was the Stanley Cup, fittingly enough on the same day that the Pittsburgh Penguins would do the same just down the coast a few hours later.
Even with all the excitement Henderson provided, Ko could have wrapped up her third consecutive major on the 71st hole - the same par 3 that Henderson birdied minutes earlier. "Somehow I was able to knock it in".
The 18-year-old Canadian claimed her first major victory with a stunning birdie on the first extra hole as they both finished at 6-under 278.
Teater, the third-round leader, bogeyed the final hole for a 75 after hitting his second shot over the green.
Ask anyone who knows Henderson well, and they will say her defining strength is her ability to be mentally tough in the moment.
"It was a pretty good day for me", Henderson said after sealing her second victory on the Ladies Professional Golf Association (LPGA) Tour.
"I just kinda patiently walked up to the green". Britt [Henderson's older sister, caddie, and fellow pro golfer] told me it was like 10 feet past the pin. "To get that world ranking up to No. 2 is kind of surreal, kind of unbelievable, but I still have one more spot to go".
Three feet from the hole kind of nice. But Ko missed her opportunity for birdie.
"I don't know whether I thought it would come true", she said.
She became the second-youngest victor in a major championship, with Ko the youngest previous year in the Evian Championship in France. She opened this tournament using a brand new Ping putter, and it worked well.
Ko took a one shot lead into the final round and led for most of Sunday before Henderson made a late move.
"I made so many putts", she said, with a bit of a laugh. She's scheduled to play the Meijer LPGA Classic in Grand Rapids, Mich. "They had the tees up on a couple of holes ... where I could go for the par 5s in two (shots)".
The world's No. 1 golfer just tipped her hat to one of the best closing rounds in women's major championship golf history - mainly because it beat her at almost her best.
Her father, Dave, is her coach, but he wasn't there on Sunday.
Henderson has been looking up to Ko for a while, using her for motivation.