Federer Nadal semi final could dictate who is the greatest

Respect: Rafa or Roger?

So nowadays Rafael Nadal and Roger Federer are contesting semi finals, rather than finals, but this could perhaps be more significant than any of the previous encounters when it comes to where each will be placed in the pantheon of the greats.

With Novak Djokovic out following his surprise defeat to Stanislas Wawrinka, the winner of tomorrow's clash will be the clear favourite to take this year's Australian Open title on Sunday.

Should Federer claim his first Grand Slam in almost two years, his longest spell without one, he would gain his 18th career Slam, a seemingly unassailable lead over Nadal, who has 13, especially given the Spaniard's injury record.

However, should Rafa prevail the pendulum would swing in his direction, being just three behind his great rival and almost five years younger than the Swiss.

Both have won all four slams at one point in their career and though Rafa has the distinct advantage when it comes to their head to head record, 22-10, Federer will often have an edge in any argument over a pint given his overall number of Grand Slam titles won.

Perhaps this is a little premature as no one can tell quite what the future will hold in this unpredictable sport (who would have anticipated Djokovic breaking the aforementioned's duopoly) but this match could just give us a definitive answer to who is the sport's greatest ever player.