"Thankfully I wasn't too nervous tonight", the 37-year-old Swiss noted. "I think that settles my nerves there", said the second seed.
Federer, though, seems as determined as ever to compete for the title and, although it would not be a huge shock to see Paire pick up a set here, that is likely to be as good as it gets for the Frenchman as Federer marches on at Flushing Meadows.
"You don't want that (loss) to happen next year".
The seventh-seeded Cilic, who said it was "one of the most brutal days that we had so far this year", told reporters the heat, plus the pressure of the shot clock introduced at the tournament this year, had proved challenging.
Nishioka rallied briefly at the end, denying Federer the chance to serve out the set and battling back to 5-4 with his first break of serve. Cîrstea has never made it past the third round - will this be the year that record gets rewritten?
Where is Benoit Paire vs Roger Federer taking place? It was as simple as you expected from Federer as he continued to just hit victor after winner and force his opponent into overplaying as he was quickly out to a two sets to love lead.
Doug Pederson lashes out at media in awkwardly tense press conference
The news of Foles starting comes a day after John Clark of NBC 10 cornered the surgeon who repaired Wentz's knee, Dr. Pederson responded to the remaining media questions with "I'm not going to discuss it", and "next question".
"It was a tough one", the world No. assured. No14 seed Fabio Fognini lost to John Millman, 6-1, 4-6, 6-4, 6-1, who will play Mikhail Kukushkin.
With temperatures soaring above 90 Fahrenheit (32C) amid crushing humidity, the United States Tennis Association (USTA) said the 10-minute heat break that women players are granted between the second and third sets would be extended to the men. The 21-year old star will next play fellow German Philipp Kohlschreiber, who beat an exhausted Matthew Ebden, who had needed 3hrs 40mins to beat No32 seed Filip Krajinovic, in the first round.
Wozniacki was the runner-up at Flushing Meadows in 2009 and 2014.
The WTA's heat rule is in effect at the U.S. Open, allowing female players a break between the second and third sets. Interesting, they have played nine sets against each other and eight of them ended with a tiebreaker.
Earlier on Tuesday, a fan collapsed in the stands at the sun-exposed court 17 during Czech Petra Kvitova's win over Yanina Wickmayer, causing the chair umpire to halt play while emergency medical personnel attended. The first break point of the match came in the eighth game of the second set and Roger saved it with a service winner to stay on the positive side of the scoreboard and he claimed the tie break with a backhand return winner and another service winner in the final point.
Djokovic is now in US Open second round action against Tennys Sandgren.