The 24-year-old bounced back from two bogeys and a double bogey to birdie three of the final five holes to secure a one-shot win over American Sophia Schubert under 17.
Her 12th victory on the LPGA Tour extends her lead as Canada’s most successful female golfer.
On a decisive day when just two shots separated Henderson from the five players tied for third under 15, his even par 71 scored his highest score after carding 64, 64, 68 in the front three days.
“It was definitely an interesting day…not the start I wanted,” Henderson said. “I remained quite patient, as patient as possible under these circumstances.
“The saying is ‘the majors are won on the back nine on Sunday’ so I just tried to keep that mindset and knew I was still in if I could get a strong back.”
The world No.10 had held a two-stroke advantage on Sunday, but a slow start opened the door for a string of players to enter contention.
Schubert advanced to the 12th, but Henderson clawed his way back to level the American before the final hole.
Disaster struck when her tee shot snuck through the trees as Schubert made the green for a birdie, but the Canadian again recovered superbly to escape trouble. And when Schubert’s putt rolled excruciatingly around the cut, Henderson was left with an 8-foot birdie chance to avoid the playoffs.
Henderson was not mistaken, heading home to take the win before being showered with champagne and water by her teammates and her sister Brittany, who caddyed for her.
“To sit here a major championship twice is just an unreal feeling,” she told reporters.
“In 2016, winning the first major changed my life. My world ranking skyrocketed and I just got a ton more attention from fans and the media. It also made me feel like I really belonged here and that I could fight for big, big championships and compete against the best in the world, which is an incredible feeling.
“It’s been a long time and I started fast this week, it was great to be top of the leaderboard for a major tournament. I just tried to push that excitement as far as I could.”
Her $1 million payout to winners brings her career earnings to $10,237,150, making her the 24th player in LPGA Tour history to break the $10 million mark, according to the LPGA.
“I want to cry tears of happiness”
After taking a short break from the game, playing no LPGA events in May, the Canadian has since won two events in four outings following his win at the ShopRite LPGA Classic in June.
“I worked a lot with my sister and also with my dad, who is my coach,” Henderson said.
“And the time with my mom at home, it really helped me take a step back and put my head in the right place so I could get back on tour and compete.
“I’m really excited for what the rest of the season has in store for us,” she added.
For Schubert, the 2017 United States Women’s Amateur Champion, it was an agonizing end to what had been a hugely impressive performance in her second major as a professional.
“I want to cry. I want to cry tears of happiness,” Schubert told reporters.
“I’m proud of myself, proud of everyone who helped me get to this point. It came just short, but I know I’ll be back so I’m really happy.
“It’s something I’ve always wanted. I knew I could do it. There was a bit of doubt, but I couldn’t be in better company.”