Even though Rafael Nadal [ Images ] is on top form, the Spaniard acknowledged he would have his work cut out to beat world number one Roger Federer [ Images ] in Saturday's Masters Cup semi-final.

"He (Federer) is playing at his best level," the world number two told reporters after overcoming Russian Nikolay Davydenko [ Images ] 5-7, 6-4, 6-4 in the Gold Group on Friday. "He is playing unbelievable.

"It's going to be very tough tomorrow but I am going to give 100 percent. I feel I am giving my best performances for a long time."

It will be the sixth occasion Nadal has met Federer this year and the winner will go on to meet holder David Nalbandian [ Images ] of Argentina or American James Blake [ Images ] in the final.

Their five previous meetings were in finals, Nadal winning the first four at the French Open [ Images ], Rome, Monte Carlo and Dubai [ Images ] before losing out to the Swiss at Wimbledon [ Images ].

Nadal's form dipped after Wimbledon while his rival's game has risen to new heights. The 25-year-old Federer has gone 27 matches without defeat.

Federer, who lost to Nalbandian in last year's Masters Cup final, said his confidence was high after beating Ivan Ljubicic in the Red Group on Thursday.

"I'm pretty happy with the way I'm playing," said the Swiss. "My serve was getting reliable on the big points and that's always a good sign."

Nadal said the indoor court favoured Federer.

"Every match is very tough," he said. "Sometimes I win, sometimes he wins.

"But tomorrow is difficult, we're playing on a hard surface. It's not the same as Wimbledon and not clay."