Roger Federer is the greatest tennis player of all time, and his 19 Grand Slam titles are testimony to the dominance he has enjoyed in a career which has spanned just under 20 years.

And, having turned 36-years-old earlier this month, Federer's remarkable tennis ability has shown no signs of wavering.

The Swiss legend has already won two majors this year, having been triumphant in Australia in January and at Wimbledon in July.

He is also the heavy favourite to win the US Open this year, in what would be his sixth triumph in New York having won five straight titles between 2004-2008.

And, he remained on track to claim a third major title of the year when he disposed of Frances Tiafoe on Tuesday night, although proceedings were not as straight forward as expected.

The plucky American youngster showed great fight and determination to take his opponent to five sets, but he came up just short as Federer prevailed 4-6, 6-2, 6-1, 1-6, 6-4.

After eventually disposing of his opponent, the reigning Wimbledon Champion would undoubtedly have breathed a sigh of relief having survived such a massive scare.

Nevertheless, the 36-year-old was in good spirits after the game, and an exchange with a young fan following his victory reminded everyone why Federer is regarded as one of the most popular tennis players of all time.

The Swiss star is considered the greatest player of all time, and thus has earned the title of 'GOAT' (Greatest of all time) from fans.

However, youngsters could be forgiven for being unaware of the acronym, and this fan in particular could not work out why the Swiss legend was named after an animal.

In typical Roger fashion, he was modest in response as he attempted to answer the youngster's question.

The full exchange went as follows: 

Kid: ‘I wanted to ask you, Switzerland is really cool, right?
Federer: Not always, but most of the time
Kid: There isn’t too much livestock. So why do they call you the goat?
*laughter*
Federer: I don’t know! Some fans call me that. I don’t call myself that. But yeah we have a lot of animals in Switzerland and goats are part of the livestock we have over there, yes.

The youngster then begged Federer to play on for another eight to nine years so that the two could compete against each other when he turns professional.

Kid: I have a serious question. You have been the most consistent player of all time. Can you please continue to play for eight, nine years so I can play you when I turn pro?
Federer: Yes. If you make it on Tour, then I’ll make sure that maybe I’ll come back for you, ok?
Kid: Is that a promise?
Federer: Almost. Almost a promise. A Pinky promise.

This conversation is just another example why the vast majority of tennis fans adore Roger Federer.

The world number three will continue his quest for a third major of the year when he plays either Mikhail Youzhny or Blaz Kavcic for a place in the third round of the US Open.