Why Andy Murray has got under the skin of Federer

What's going on with Roger Federer? So begrudging in his praise for Andy Murray in the past, the world number one has suddenly changed his tune and said the 22-year-old Scot has a good chance of winning the US Open, currently taking place at Flushing Meadows in New York. It would be Murray's first ever Slam title.

Federer said yesterday: "I think Andy deserves a few picks [as potential champion] because he is playing so well. He is in the best shape of his life right now. He did well last year and he has got one more year of experience. The only thing is he hasn't won a Slam yet, but he's still quite young."

This is the same man who, at the Australian Open in January, expressed shock bordering on contempt when Murray was installed as pre-tournament favourite by some bookmakers. 

"He's the favourite?" asked the 13-times Slam winner incredulously (he had yet to win his 14th at the Roland Garros and his record-breaking 15th at Wimbledon). "Good for him. It won't help him a whole lot. It surprises me that the bookies would say that because he hasn't won a Slam yet. Novak Djokovic won here last year. Rafa had an incredible season last year. I won the last Slam of last season so it is surprising."

So what could have prompted the Swiss champion’s volte-face?

Well, Murray has had his finest season to date, registering back-to-back quarter-finals in Melbourne and Paris, and reaching the semi-final of Wimbledon, where he lost to an inspired Andy Roddick. He has also picked up five ATP titles this year.

But beyond the mind games that all great sportsmen employ against their opponents - Federer is merely cranking up the pressure before Murray’s easy match against Chilean Paul Capdeville in New York tonight - Lawrence Donegan in the Guardian has an intriguing theory.

"There is just something about Murray that appears to get under the skin of the world number one," writes Donegan. "Perhaps the Swiss is baffled so much attention is heaped on a player who has yet to win a Grand Slam, or it could have something to do with the fact the Scotsman is one of the few players who hold winning career records (6-3) over the greatest player of the modern era." Quite. ·