So Yeon Ryu (70 on Sunday) finished third, four shots back of Hall.
Should Higa win the tournament, she will become only the second Japanese to capture a major. His grandmother is one of his biggest supporters who navigated her way around the hills of Firestone using a walker in 90-degree heat.
"I had so much support today from all the people backing me and supporting me and cheering my name", Hall said.
"I just got a huge knot in my throat and I just had to put my head down", he said after closing with a 1-under 69 for his first World Golf Championship title.
England's Georgia Hall kisses the trophy after she wins the Ricoh Women's British Open at Royal Lytham & St Annes Golf Club.
Georgia was born during the 1996 Masters won by English golfer Nick Faldo at Augusta, Georgia.
Hall took up golf at the age of seven and quickly rose up the junior and amateur ranks.
That same year, Hall represented Team GB at the 2013 Youth Olympic Festival where she won two golds and was part of the European team at the Junior Solheim Cup. The galleries roared for the homeland woman as she made her way around the course.
If it is any consolation it was Lee's second best finish in five starts at the Women's British Open having finished 9th in 2015.
Hall sealed a two-shot victory thanks to a final-round 67 at the famous Lancashire links venue, a place where golfing legends, Bobby Jones, Tony Jacklin, Gary Player and Seve Ballesteros have all sealed Open Championship glory.
He marked his ball, turned toward the back of the green and saw his grandparents, Paul and Phyllis Thomas, who had never seen him win since his joined the PGA Tour.
But Hall chose the flawless moment to showcase her best golf and took the lead at exactly the right moment, sinking a ideal 20-foot putt on the sixteenth after Phatlum had found the green-side bunker. Her short game was the key to her victory.
The Bournemouth golfer is just the third home victor since it became a major in 2001, following Karen Stupples (2004) and Catriona Matthew (2009).
When Georgia Hall pulled even with Pornanong Phatlum with birdie at the 13th, the final round went to match play.
And a two-player race for the year's fourth major was definitely established when both picked up a shot at No. 4 and Phatlum followed Hall in birdying No. 6.
The large lead allowed Hall to enjoy the rousing reception she received on her victory march up to the final hole, where a three-putt bogey was academic.
A wobble in the sand on the 14th almost saw Hall lose all the progress she made on the front nine, but Hall managed to make par.
Hall added another birdie at the par-four 16th to take sole possession of the lead, before going three shots ahead when Phatlum double-bogeyed the 17th after driving into a fairway bunker.