Roger Federer returns a shot during his US second round win over Mikhail Youzhny. Photo: AP Photo/Andres Kudacki

NEW YORK - Andy Murray has a hip injury, Novak Djokovic is sidelined with an elbow problem while Stan Wawrinka needs knee surgery, but Roger Federer insists it could still be years before the old guard say goodbye to tennis.

While 18-year-old Denis Shapovalov and Andrey Rublev, 19, have kicked the US Open door slightly ajar this week, 36-year-old Federer doesn't see the pair supplanting him or his fellow Grand Slam kings anytime soon.

"The changing of the guard is going to come at some stage. Could very well be next year. But I still predict it's going to take a few more," said Federer on Thursday.

Many see this US Open as the most unpredictable in years. But highly regarded 20-year-old fourth seed Alexander Zverev and number seven Grigor Dimitrov both failed to get beyond the second round and that kind of inconsistency has Federer believing that the sport's 30-somethings will still be a force in 2018.

"I'm not sure if 2018 is going to be wide open just because we don't know how a lot of those top guys are going to come back," he said after making the US Open last 32 on Thursday with his 80th career win at the tournament.

"What I think is that it's going to be interesting is that their ranking is going to be all over the place. We're going to see some interesting draws, to say the least."

Federer pointed to the examples of himself and old rival Rafael Nadal at the Australian Open this year. Injuries and loss of form saw him seeded at 17 and Nadal on nine.

However, they still made the final with Federer winning the title before adding an eighth Wimbledon trophy in July. Nadal, for his part, claimed a 10th French Open and has since regained the world number one ranking.

"We had a little bit with me and Rafa down in Australia. But now we're talking probably about a bigger group," added Federer of his and Nadal's situation in Melbourne.

"That's going to go down maybe all the way to Murray, as well, depending if he's going to be playing at all for the rest of the season. He's got a lot of points to defend. 

"If that's the case, he might drop further down outside of the top four, then things are going to look real weird. I think it's going to be very interesting."

Federer needed a second successive five-setter to reach the US Open third round with a 6-1, 6-7 (3/7), 4-6, 6-4, 6-2 win over fellow veteran Mikhail Youzhny of Russia.

It was his 17th win in 17 matches against Youzhny in a rivalry stretching back to 2000.

Five-time US Open champion and third seed Federer had also needed five sets to see off US teenager Frances Tiafoe in the first round.

The 36-year-old will face another 35-year-old in Feliciano Lopez for a place in the last 16. His record against the Spaniard is just as solid - 12-0.

"It was quite a lot of fun out there - I feel quite warmed up by now," said Federer.

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