The 17-year-old world No 1 from Switzerland beat the 11th ranked Spaniard 6-3, 6-3 in 86 minutes to take the fourth major of her career.
Hingis dominated from the start, breaking the 25-year-old Spaniard's first service game, to the finish when Martinez put a backhand wide to lose her serve again.
But the Swiss youngster, who also won the women's doubles title on Friday, insisted this was the most difficult and most satisfying of her four majors.
Hingis said: "It was very different, a lot harder than last year because there were so many different expectations of me and pressure, especially from myself because I really wanted to defend the title."Reuse content