Will Federer catch Nadal? (Picture: Getty)

Roger Federer played down his chances of replacing Rafael Nadal as world No. 1 in 2018, despite still having the chance to move within 140 points of his Spanish rival by the end of the ATP Finals.

The world No. 2 kept the heat on the 16-time Grand Slam winner with a victory over Marin Cilic at the O2 on Thursday afternoon, and will now earn a mighty 1500 points as an unbeaten champion if he secures success in his next two matches.

While Federer doesn’t want to get too far ahead of himself in London, he feels that even if he does overcome both remaining obstacles Nadal remains in a strong position due to the 2,000 points dropping off at the start of next year courtesy of his 2017 Australian Open triumph.

And he is convinced that if he focuses on it too much and it becomes a realistic goal, he may well slip up and miss out.

‘I have 2,000 points to defend in Australia, he doesn’t. So there’s the problem already,’ he said after his win against Cilic. ‘I know he has a lot of points to defend, too, in Australia, but not as many as me.

Will Federer catch Nadal? (Picture: NurPhoto/Getty)

‘That’s why I always said, look, it’s not a realistic goal in some ways, you know, world No. 1. It is interesting. It’s the ultimate achievement in tennis in some ways, it always has been for me.

‘But at this age, it just can’t be because I think I’ll make mistakes if I start chasing it. I’m not sure how much the body allows me to chase goals like this.

‘Maybe if I start thinking about it too often and too much, I think I’m maybe also not playing the way I’m supposed to be playing, maybe I tense up, maybe I’m nervous, maybe that’s not good for my back. Who knows what it is.

Federer still has a lot of work to do (Picture: AFP/Getty)

‘Still far away from being close in the points with Rafa. Still need to win this tournament before it’s actually really close. I’m only in the semis. The big points are really coming in now. So that’s why my focus is on the semis. If I would win that, of course it’s just on the finals.

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‘The year played out the way it did, and Rafa was better. He deserves to be there. I’m really happy for him because he had a rough season as well in ’16. It’s great for him.

‘Then in Australia, I just hope to be fit again, to walk out on Rod Laver Arena and hopefully defend my title. But still very far away at this point.’