Roger Federer is in no doubt that Novak Djokovic deserves to finish 2012 as the world's top-ranked player.
Federer replaced Djokovic at the top of the standings after winning Wimbledon in July but ceded the No 1 position to the Serb yesterday.
And with the Swiss star unable to improve on last year's perfect performance in winning the 2011 season-ending ATP World Tour Finals in London, not even an unblemished victory this year at the O2 Arena will see him regain top spot before 2012 is out.
"We know who the real No 1 is," said Federer. "It is going to be Novak. I do not think there should be any debate around about that.
"You do not get to No 1 by chance. The rankings are something that shows how you have played over a 365-day period. It might all change again in two months at the Australian Open but right now it is clear."
Federer all but conceded the No 1 ranking this year when opting out of defending his Paris Masters title last week on the grounds he could not do himself justice by playing successive tournaments in Basel, Paris and London.
"I obviously gave it everything I had," said Federer. "I've played so much tennis the last one and a half, two years and I'm happy I got back to world No 1."
"It's obviously a time where you need to win at least a slam, if not more slams, or at least five to 10 titles, so we're not talking about just a quick jump to No 1 and then you lose it again."
"This is a full-on process. That obviously takes a lot of sacrifice. For the time being, I'm willing to do all of that."
Although Djokovic has, unsurprisingly, failed to hit the same heights as in 2011, when he won three out of the four grand slam singles titles, this year has seen him retain his Australia Open crown and reach the finals of both the French and US Opens, losing the latter to Britain's Andy Murray.
Fatigue caught up with Djokovic in London last year and he suffered a shock loss to American Sam Querrey in Paris.
And the 25-year-old Djokovic said it was tough to be in peak shape at this stage of a long season.
"It is expected not to be always in your top form at this time of year," he said. "The effects of the long season can influence you physically and mentally but this is an important tournament and I definitely want to do well."