David was at the brilliant best as she shut out Duncalf 11-8, 11-4, 11-6.
The world number one took control from the first game, jumping out to a 6-1 lead, and although Duncalf fought back to level terms the Englishwoman was always playing catch up and David never looked like relinquishing her grip.
"I knew that today was going to be a tough final, she knows my game really well and we play each other a lot," David said.
"I really had to stay consistent in there, I was moving well, I focused well and I just stayed on my game."
In the men's final, Ramy Ashour became the first Egyptian to win the title when he beat England's defending champion Nick Matthew in five games in a magnificent contest.
Ashour and Matthew fought each other almost to a standstill before the Egyptian pulled away in the decider to down the world number one 12-14, 11-6, 10-12, 11-8, 11-4 in a match of the highest quality.
Both men played some spectacular squash throughout the final but the 23-year-old Egyptian finished stronger than his opponent and was a deserving winner.
Matthew had gone into the match as the slight favorite following his impressive semi-final win over David Palmer on Saturday.
And he looked every inch the champion as he opened up a 10-6 lead in the first game and held off a comeback from the Egyptian.
Ashour leveled the match in the next game before Matthew got his nose back in front, again having to hold off an Ashour comeback.
But Ashour fought back again to win a tight fourth game before exploding in the fifth, controlling the front of the court and hitting a string of winners.
"It’s such a great thing to win the Australian Open, I’ve been thinking about this since last year when I lost to Nick," Ashour said.
"It’s one of the biggest names on tour, to win the Australian Open, so I’m glad to join those great players on the trophy.
"The match was tough for both of us both physically and mentally, but I think he had a little bit more pressure on him because he’s number one."
Matthew said one poor game had cost him the match, but paid tribute to Ashour’s fighting spirit.
"Everyone gives him credit for his shot-making but some people forget he’s got that side to his game as well, that makes him such a champion," he said.