Saina beat Yamaguchi 21-12, 22-20 in straight sets.
This this the third title for Nehwal this year. With this win, Nehwal becomes the first Indian to win the China Open Super series.
Nehwal wrapped up the game in 43 minutes as she beat her opponent in straight sets 21-12, 22-20 to lift the trophy.
She had earlier this year won the Syed Modi International Grand Prix Gold and the Australian Super Series in June.
In her sixth appearance in the prestigious tournament, Saina had to draw from her reservoir of experience to stave off the challenge of the athletic Akane.
Saina beat Yamaguchi 21-12, 22-20 in straight sets
In the opening game, Saina led 3-1 early on and extended it to 8-4. She lost few points due to miscued strokes but the Indian managed to go into the interval with a four-point lead with the help of an angled stroke and down the line smash.
Saina controlled the shuttle and the pace of the game and forced her young rival to commit errors, opening up a healthy 14-7 lead.
Akane showed sparks of brilliance but it was not enough to threaten Saina, who moved into game point with a delicate net shot and then a disguised return to earn the bragging rights.
Akane produced a better performance in the second game. The 17-year-old was quick on her legs and bothered Saina with her straight smashes to enter the break with a slender 11-9 lead.
(With PTI inputs)