NEW YORK—Roger Federer pointed to his recent back injury when explaining his poor start to his first-round match at the US Open, saying it limited his training.

Federer dropped the first set to 19-year-old Frances Tiafoe and had to win a tight fifth set for the victory. He was playing his first match since being hampered by a back injury in the final of Montreal.

"I don't think I had the preparation I was hoping to get," said Federer. "Since Montreal, 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 was hoping to start better."

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Federer dropped the opening game, hitting some unforced errors, and could not get back into the first set.

"I think I was also being a bit cautious with my movement. Then, in the second set, I think it all started to come together. That was good," he said. "But because of the preparation being not the best that I've had, I think I was quite up and down. Every time I was down, Frances took care of it. Then in the fifth, it was just more of, 'Get the energy back.' You know, play to win."

Even with the uneven start, the No. 3 seed expects the back to improve during the tournament.

"I'm very happy how I'm feeling right now, how I felt coming off the court. I think there's a lot of positives for me to look at," he said. "I think this will actually give me a lot of confidence. In the first set, really, I was just seeing and feeling it, see how far I could push, but I was never in pain. It was OK. That's why when I was down a set, I just said, 'OK, the match starts here.'"

Federer is a five-time champion at the US Open, played at Flushing Meadows.

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Roger Federer: Back injury contributed to 'rusty' start at US Open

Roger Federer: Back injury contributed to 'rusty' start at US Open

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