If he gets through that, then a first-ever showdown in New York against Federer would move a little nearer, although the Swiss legend has to defeat Spain’s Feliciano Lopez in his third-round clash.

Nadal had also dropped the first set of his second-round match against Japan’s Taro Daniel before winning in four.

Saturday was almost a carbon copy with the 15-time major winner unable to convert any of six points in the opener.

But the match turned in the 10-minute seventh game of the second set when, on his 14th break point of the encounter, he finally smashed his way through.

There was no way back for Mayer, who ended the match with 52 unforced errors and his record against top 10 opponents at 1-25.

“It was a long day,” said Nadal who brought the curtain down on the day session at 8.40 p.m. and under the Arthur Ashe Stadium roof.

“It was tough. I had 14 break points – that’s not a good figure. But I was there mentally and fought a lot at the right moments.”

Five-time champion Federer faces Lopez boasting a 12-0 record over the 31st seed, who is playing in a 16th straight US Open and 63rd successive grand slam.

Federer has struggled so far, needing back-to-back five-setters to defeat Frances Tiafoe and Mikhail Youzhny.

Germany’s Phillip Kohlschreiber eliminated Australia’s John Millman 7-5, 6-2, 6-4 and will face either Federer or Lopez.

Kohlschreiber has a 0-11 record against Federer.

“I hope Feli wins,” smiled the 33-year-old German.

Austrian sixth seed Dominic Thiem defeated France’s Adrian Mannarino 7-5, 6-3, 6-4 to make the last 16 for the third time in four years.

Thiem next faces 2009 champion Juan Martin del Potro of Argentina, who put out Spain’s Roberto Bautista Agut 6-3, 6-3, 6-4.

Russia’s Andrey Rublev became the second teenager in the last 16 when he beat Bosnia’s Damir Dzumhur 6-4, 6-4, 5-7, 6-4.

Rublev, just 19, faces Belgian ninth seed David Goffin who progressed when 2016 semi-finalist Gael Monfils retired with a right knee injury.

Women’s top seed Karolina Pliskova saved a match point to defeat China’s Zhang Shuai, hanging on to her world number one spot in the process.

Top seed Pliskova, the runner-up in 2016, triumphed 3-6, 7-5, 6-4 but was forced to save a match point in the 10th game of the second set and recover from a break down in the decider.

“I was match point down and I thought I haven’t tried many forehand winners down the line. That’s what I did. I may not have got another chance,” said the 25-year-old, who will face American Jennifer Brady for a place in the quarter-finals.

Had she lost on Saturday, Pliskova would also have been guaranteed to lose her world number one ranking to either Wimbledon champion Garbine Muguruza or Elina Svitolina.

Ukraine fourth seed Svitolina stayed in contention for the top ranking with a 6-4, 7-5 win over Shelby Rogers of the United States.

Russia’s Darya Kasatkina reached the last 16 of a major for the first time by seeing off French Open champion Jelena Ostapenko, the 12th seed, 6-3, 6-2.

Meanwhile, controversial Italian Fabio Fognini was kicked out of the US Open for making foul-mouthed comments to female umpire Louise Engzell during his first round loss to Stefano Travaglia.

Fognini and compatriot Simone Bolelli had reached the third round of the men’s doubles but tournament organisers have now axed him from the event.

Fognini, the world number 26, was also fined $24,000.