Roger Federer suggested his sluggish display in Monday's first-round win over Indian qualifier Sumit Nagal at the US Open was "not a bad thing".
The Swiss third seed, a five-time champion in New York, produced 19 unforced errors to surprisingly drop the first set against a player ranked 190th and without a tour-level win.
The 38-year-old recovered to progress 4-6, 6-1, 6-2, 6-4 and clinch his 1,224th career victory that set up a meeting with Bosnia's Damir Dzumhur.
"Maybe it's not a bad thing to go through a match like this. It was very similar at Wimbledon when I dropped the first set there, as well, in the first round," said Federer, who lost a five-set epic to Novak Djokovic in last month's final at the All England Club.
"At the end you look at the last three sets, and they were good. That's encouraging."
A dismal first set served as a wake-up call for Federer, who is now 62-0 in Grand Slam first rounds dating back to the 2003 French Open.
"I broke every time first game each set. That was good. I think trying to forget the first set is never sort of easy I guess in a first round, under the lights. People expect a different result. I expect something else," he said.
"I just wanted to pick up my game really, start to play better. I was able to do that. That was a relief, going up 3-0 in the second set, realizing that it is in my racquet, how I also felt it in the first set.
"The thing is I wasn't serving consistently enough. I was hitting double-faults that usually I don't do. Also I was just hitting too many unforced errors. I was in two minds, I guess."
Federer's victory saw him qualify for a record-extending 17th ATP Tour finals appearance, although he wobbled as he served for the match in the fourth set, a struggle reminiscent of last month's Wimbledon final when he squandered two championship points.
"I thought he was getting a bit down on himself naturally after set two and three. That's why it was key to stay ahead, and I did," Federer said.
"You have to get over the finish line. I got that the hard way in Wimbledon. He did a good job to stay with me. I had to close it out. That was a tough last game. Maybe exactly the kind of service game I needed to serve it out."
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