When the impenetrable Bjorn Borg was playing impeccable tennis, his Romanian rival Ilie Nastase declared: "They should send Borg to another planet. We play tennis, he plays something else." No one knew how to beat Borg then, no one knows how to beat Novak Djokovic now. In the press box yesterday, when I asked a respected writer what Roger Federer needed to beat Djokovic, his reply was fitting. "A machine gun," he said dryly.

In more practical terms, what the peaceful Swiss requires in Thursday's semi-final encounter is the first set. This is a unanimous decision. Magnus Norman, whose protege, Stan Wawrinka, was the last man to defeat Djokovic in a Grand Slam, says: "It's more important for Roger to win the first set. The longer the match, the more it favours Novak."

Wayne Ferreira, former world No.6 and twice an Australian Open semi-finalist, concurs. "Very much so," he says of Federer needing the first set. "If he's behind he feels it's too big a mental battle." Todd Woodbridge, the legendary doubles player and singles semi-finalist at Wimbledon, goes further: "For Roger to win he has to win the first two sets. A set-all favours Novak."

Federer and Djokovic have played 44 times and won 22 times each and yet dig within these numbers and they lack a true symmetry. In the last 11 meetings, Djokovic leads 7-4 but more tellingly he has won all their Grand Slam meetings in this period (Wimbledon finals in 2014, 2015; US Open final 2015) and also their two finals at the Barclays ATP World Tour Finals. At the bigger events, the younger man has been the better man.

Bob Brett, who once tutored Djokovic's coach, Boris Becker, believes the Serb is at a "different level". But in sport there's always a chance and small things suit the Swiss. The court, says Norman, "is good for Roger because it's a little quick. And he also saved a lot of energy (by losing only a single set in five matches)".

Yet what Federer needs most - and here, too, there is unanimity - is balance. An offensive mindset yet also patience. Attack, but at the right time. Or what Ferreira calls a "conservative aggression". Adds Norman, "it's a balance between not being too defensive and not overplaying. To not go all the time but to believe when you do go."

Woodbridge insists the Swiss must "remain patient and not panic when it gets tight. He needs to go for his shots but he has to set up the play. On big occasions he goes too early sometimes. Novak makes you feel you need to hit the lines, but you don't have to hit the lines."

Djokovic the magnificent hits every stroke well, meets every occasion strongly and moves fast over long periods. It means Federer, six years older than his rival at 34, needs to be almost perfect. Brett's suggestion is for "Federer to take time away from Novak by playing close to the baseline". And for the Swiss to use his short, backhand slice or even semi-drop shots to "take Djokovic out of his comfort zone".

Federer's team of Severin Luthi and Ivan Ljubicic will be planning new strategy. Perhaps part of it might involve a phone conversation to his pal Wawrinka, who played blinding tennis to beat Djokovic in the 2014 French Open final. It is possible to outplay the Serb but as Norman explains, "(Stan) was feeling the ball that day and it's tough if you're not feeling the ball".

Feel, fun, calm, balance, the crowd, the first set, Federer needs all this. Yet no one dismisses his chances because no one dares to. And so, despite the odds and record favouring Djokovic, Norman still says: "It's an open match." Seventeen Grand Slam titles is not a greatness to underestimate.