It might be said that the major string instruments on this planet include the violin, lyre, cello, viola, harp, mandolin and Roger Federer's racket. People come to see him win but also for the music. For the humming backhand slices, the buzzing forehands, the rhythm, the tempo. Some nights he's in a contest, on others like Tuesday under the stars he gives a concert.

Relaxed, smooth, controlled and hitting high notes at whim - 25 winners on the forehand, 21 on the backhand - he dismantled Mischa Zverev 6-1, 7-5, 6-2 in 92 minutes. Andy Murray may be No.1, but Zverev, who beat the Scot, said of Federer: "It's hard to read where he is going."

We can at least inform you that the Swiss has gone straight from the semi-finals of Wimbledon 2016 to the semi-finals of the 2017 Australian Open with not a single tour match in between. No wonder there was a fan who alone sang his name as if it were a hymn.

You can't practise focus in training. You can't prepare for big moments in practice. It requires matches to tune the mind and ready the legs. But Federer seems the exception to all rules. So while superbly fit champions have been ejected from this Open, this four-child papa, all of 35, with body parts which you'd think are reaching their athletic use-by date, is in contention for a Slam? In a harshly competitive era it is almost unthinkable. Even, apparently, to him.

"I felt I was always going to be dangerous on any given day in a match situation," said Federer. "But obviously as the tournament would progress, maybe I would fade away with energy. I think now that I'm in the semis, feeling as good as I am, playing as good as I am, that's a huge surprise to me."

Now this well-preserved tennis fossil is in his 13th Open semi-final (the next best is eight) and his 41st Grand Slam semi (the next best is 31). Best to leave it there for the Wikipedia page on just his career statistics has 16,000 words. If all this isn't intimidating enough, playing him at a Slam, as Zverev discovered, can be a deeply unfair business.

First Federer's CV is read out (88 titles to Zverev's 0), then he hits three clean winners in the first service game, only to be followed, without any irony, by the crowd singing "Let's Go Roger, Let's Go".

Really?

But it is this affection for Federer, from a wide spectrum of folk, which is always fascinating. He's cried in Australia and still this hard land adores him. Perhaps because he's not some moody, remote artist, but an engaging and affecting man who is at once extraordinary and ordinary, gently vain yet respectful of his peers and the game.

An Australian colleague who had to take her child to a children's hospital recently, noted that every time the doctors passed the TV, on which Federer was playing, they would say, "How's he doing? Winning! Great." Another colleague, Greg Baum, The Age newspaper's skilful columnist who shuns overstatement, wrote that achievement, style and graciousness define the great sportsman and that "only in one man are they combined peerlessly and inimitably".

Jimmy Connors and John McEnroe probably don't send roses to each other but even Federer's rivals bring warmth and awe to any discussion him. Andy Roddick, who will be enshrined in the Hall of Fame this year, yesterday noted that "I appreciate his respect that he's shown me throughout the years".

But most charming was the journalist who sits at the desk beside me in the press room. Filip Dewulf was a French Open semi-finalist in 1997 and three years later played Federer in Copenhagen. His smile tells you he will never forget the experience. Even defeat against Federer can be memorable.

"His game is so smooth, so easy," said Dewulf. "His technique is perfect, it's like from a book. He's testing you all the time, making you play strange balls, attacking you all the time, making you do stuff you don't want to do. I love to watch him. There's always something happening."

Yesterday, against Zverev, Federer brought forth his entire palette of colourful shots and he will need even more on Thursday for he collides with a player who learnt from him, has beaten him, and has won more Slams than him in recent times.

Stan Wawrinka used to be fluent on clay but is now a threat everywhere, a transformation that Federer sportingly saluted: "I think he's done incredibly well on all the other surfaces. He's become such a good player, I super respect that, that the guy is able to transform his game around like that, in his footwork, in his mind, also in his game plan."

It is the perfect semi-final, two friends, who guide each other - "it has been 95 per cent of me giving advice," clarified a smiling Federer - have won an Olympic doubles gold and Davis Cup title with each other, but fortunately do not play like each other. A night of contrast is promised, for Wawrinka, let us be clear, is not a man for delicate string instruments. He prefers a club.