Novak Djokovic of Serbia, hits a return to Tomas Berdych of the Czech Republic, during their semifinal round match of the 2011 Cincinnati Open tennis tournament in Cincinnati
Novak Djokovic of Serbia hits a return to Tomas Berdych of the Czech Republic during their semifinal round match of the 2011 Cincinnati Open tennis tournament in Cincinnati, Ohio, August 20, 2011. Reuters

World number one Novak Djokovic looks to make it an unprecedented six out of six in Masters series titles when he takes on Britain's Andy Murray in the final of the Cincinnati Open on Sunday but both players say their bodies are feeling the strain.

Djokovic, who has a 57-1 record this season, has already claimed nine tournaments in what has been a remarkable year of dominance in the sport and he is the clear favorite for the U.S. Open, starting in New York on August 29.

The Serb booked his place in the final with a victory over the Czech Republic's Tomas Berdych, when his opponent had to retire with a shoulder injury having lost the first set to Djokovic 7-5.

Despite only spending 52 minutes on court, Djokovic, who has some shoulder problems of his own, said that he was not in peak condition ahead of the final.

To be honest, I am definitely not 100 percent but I'm getting out there and trying to give my best to win every match I play on. I know that I felt better last week.

But I'm in another final. It's a great achievement. Tomorrow (Sunday) I'll try to get another title.

I hope it's not going to be too hot and let's hope for another good match. We have a good rivalry, same age, same generation and it's nice to play him in a final again.

Murray beat American Mardy Fish in his semi-final on Saturday but said he was hampered by fitness problems

I was struggling physically. That's frustrating for me, because that's something I haven't struggled with for quite a long time, said the Scot.

The pair met in the final of the Australian Open in January with Djokovic winning in straight sets and the Serb came out on top again in the Rome semi-finals four months later.

But Djokovic also recalled that Murray beat him here in the 2008 final - one of seven Masters triumphs for Murray.

This is a surface that he plays well on, I think, said Djokovic.

We played here in the final and had two tough sets and he won that. So he knows what it takes to win a big match, a big tournament. There is no favorite.

Murray, who has yet to win a grand slam, is under no illusions though about the size of the task facing him.

I'll need to play well to get it tomorrow, but it's the perfect test to see exactly where my game is before the U.S. Open because he's the number one in the world just now, he said.