Roger Federer has said he doesn't care about how he is playing at the US Open, only that he is winning matches.

The 30-year-old progressed through to the fourth round after a four sets win against Croatian Marin Cilic, and will now face Juan Monaco of Argentina.

"I seriously don't care how I'm playing," said the third seed. "I wish I play my best every single time and feel amazing.

"That's not reality. Anybody who goes to work knows it's not as great as he wishes to be, and we go through the same thing. But you find a way to win when maybe someone is not playing so well or when your opponent is playing well, and that's what the beauty is of this game, I think, is trying to find a way when you're not feeling great. That's what I maybe was able to do today."

The Swiss has won the Flushing Meadows event five times.