Defending US Open champion Marin Cilic has revealed that finding rhythm on his service was key to his victory against Jeremy Chardy in the fourth round at Flushing Meadows.

Cilic was able to defeat the number 27 seed in four sets with a 6-3 2-6 7-6[2] 6-1 triumph in New York, and the Croatian star has since moved to state that his performance on serve was crucial towards his win.

"The key today was finding my rhythm on the serve, especially in the third set," Cilic revealed after his victory.

"My ankle was causing me a little bit of trouble in the second set. First couple of games in the third wasn't easy. I was conscious of it."

Cilic will now take on France's Jo-Wilfried Tsonga in the quarter-final.