Roger Federer refuses to reveal whether his recent William Tell trickshot was a stunt or for real, but there was no doubting the authenticity of his latest moment of magic here at the US Open. The former world No 1's through-the-legs winner against Brian Dabul was more spectacular even than a similar stroke he hit against Novak Djokovic on the same court 12 months ago, which at the time was dubbed the "shot of the century".
The William Tell cameo – in an advert for Gillette, Federer apparently knocks a can off a man's head with a serve – has already been viewed more than six million times on YouTube but may soon be supplanted by the latest piece of Swiss sorcery.
Towards the end of the second set of his 6-1, 6-4, 6-2 first-round victory, Federer had to back-track rapidly to chase down a lob. He was a good 10 feet behind the baseline by the time he reached the ball and had time only to hit it back between his legs while still facing the wrong way.
Nevertheless, he struck the ball so well that Dabul, who was on his baseline, could only watch in amazement as it flew into the corner of the court for a clean winner. If the shot against Djokovic last year came at a more critical moment – Federer was two points from victory in a semi-final – Monday night's winner was even more extraordinary in that Dabul was at the back of the court rather than at the net.
"Maybe in terms of difficulty this one was harder, because I had the feeling I had to run a longer distance and I was further back," Federer said afterwards. "I really had to give the last big push at the end. I didn't have time to set it up. So I felt like this one was incredible again. I turned around and couldn't believe the shot had landed in the corner."
Federer said that he rarely practised the so-called "hot dog" or "tweener", but this is at least the fourth occasion on which he has hit a winner with it. He first recalls doing so against Sjeng Schalken in a Davis Cup tie in 2003 and repeated the feat against Daniele Bracciali in Dubai three years ago.
As for the William Tell video, the Swiss remains tight-lipped about its authenticity. Some players are sceptical – "There's not a chance it's real," Andy Murray said – but Federer insisted: "I can't tell you if it's real or not. That's up for debate. I'm not going to answer that question."
Federer next plays Germany's Andreas Beck, while Lleyton Hewitt, who was a potential third-round opponent, went out in the first round for the first time in 11 appearances at the US Open. The 2001 champion, who beat Federer in the final in Halle three months ago, went down 6-3, 6-4, 5-7, 4-6, 6-1 to France's Paul-Henri Mathieu in a match that lasted more than three and a half hours.
For a while yesterday it seemed that Djokovic, potentially the biggest threat to Federer's seventh successive appearance in the final, was also on his way out. Viktor Troicki, Djokovic's fellow Serb, had the chance to serve out for the match after going 3-1 up in the fourth set before the world No 3 hauled himself back to win 6-3, 3-6, 2-6, 7-5, 6-3.
Djokovic, who is seeded to meet Federer in the semi-finals, has wilted in the heat before and looked in increasing discomfort as the afternoon temperature climbed to 36C. Marcos Baghdatis was another to suffer and was beaten 6-3, 2-6, 1-6, 6-4, 7-5 by the veteran Frenchman, Arnaud Clement.
Anne Keothavong was beaten 2-6, 6-1, 6-1 by Taipei's Yung-Jan Chan but blamed defeat on her failure to deal with her opponent's moonballing tactics rather than the conditions or the foot blisters for which she needed treatment in the third set. Having fought her way back from cruciate ligament damage for a second time earlier this year, Keothavong has yet to recapture the form that saw her reach the third round here in 2008. She broke down in tears and said: "I'm not the player I was two years ago here. Who knows what will happen after this? I'm going to need time to reassess and decide what I want to do."