Roger Federer is through to the next round of the U.S Open but not in a manner you would expect from the Swiss master.

Third seed Federer battled to defeat 19-year-old American Frances Tiafoe in five sets to reach the US Open second round on Tuesday night in New York.

The 19-time grand slam winner needed 2hr 37min to down Tiafoe 4-6, 6-2, 6-1, 1-6, 6-4 to make it into the second-round. 

Later in his press conference, the Swiss was asked more questions by reporters about his slow start, Federer replied, "I don't think I had the preparation I was hoping to get. Since Montreal, the focus has been more on the back, making sure I can play the tournament rather than being well-prepared. I always knew I was going to come in feeling rusty or not great.

"I really struggled early on. I think Frances connected well. I kind of lost my footing sometimes. My eye wasn't working. I was misjudging distance. I think I was also being a bit cautious with my movement.

"Then in the second set, it all started to come together. That was good. But because of the preparation being not the best that I've had, I was quite up and down."

He was then asked about his "dodgy" back. "I'm very happy that I'm feeling as good as I'm feeling right now," Federer said. "If I had felt that my back was going to get worse every match, I probably wouldn't have played.

"My hope and my belief is that it's only going to get better from here because every day that goes by puts me further away from what happened in Montreal."