How the clay has saved Federer's top spot

Two months ago, when he was stuck in his slump, there was a real chance Federer could lose the No 1 spot to Nadal before Wimbledon.

When the ATP rankings came out on 10th March the gap between Roger and Rafa was only 350 points, the closest it has ever been. To put it context, winning a Masters Event like Monte Carlo is worth 500 points and the French 1,000 points.

Federer then scraped together enough points in Indian Wells and Miami to extend his lead to 670 points coming into the clay season.

So Nadal was within touching distance.

The problem of course for Nadal is that even if he won all the clay tournaments he would not necessarily close the gap, because he's only matching his achievements (and points) from 2007. Rafa also needed Roger to struggle on clay. Something that seemed possible given his difficulties in the US.

Which is why Federer's recent revival has been so important and impressive. 4 weeks in, point for point, it's Federer who's having the better clay court season.

Federer picked up 175 bonus points by winning Estoril, defended his points in Monte Carlo by reaching the final, and has already gone further in Rome than last year's third round exit.

Meanwhile Rafa matched his 2007 victories in Barcelona and Monte Carlo but his shock second round exit in Rome means he drops 465 points.

Which means Roger will increase his lead of 845 points over Nadal when the rankings come out on Monday, giving him a decent cushion if he drops points in Hamburg or Paris.

There's an awful lot of tennis still to come this year but if he remains at No 1 until the end of the year, he'll probably look back and regard clay as the turning point.