The Indian, ranked 71 in the world, recorded a 9-11 11-4 11-8 12-10 win in the summit clash against British rival.
Joshna started off in a sluggish manner and lost the close opening game, in which score were 8-8 at one stage.
However, in the second game, Joshna build up a 6-3 advantage and was swift in her moves, covering the court well.
The Indian took five of the six points to draw the parity, pocketing the second game in just 10 minutes.
The third and the fourth games were closes affairs as Johsna trailed initially in both but showed tremendous fighting ability to comeback and win.