Nikolay Davydenko believes he can beat Roger Federer in their semi-final clash at the Barclays ATP World Tour Finals on Saturday.

This is despite failing to do so on 12 successive occasions.

The Russian booked his last-four spot tonight with a 7-6 (7/4) 4-6 6-3 victory over Robin Soderling, who was already through.

After yesterday's shenanigans, the equation tonight was simple - a win for Davydenko would put him through while defeat would hand the second place to defending champion Novak Djokovic, who beat Rafael Nadal 7-6 (7/5) 6-3 earlier.

Davydenko proved up to the task but the set Soderling won ensured he topped the group and will meet Juan Martin del Potro tomorrow evening, while the world number seven faces a quick turnaround for an afternoon match against Federer.

Although history is against him, the pair have not met for more than a year and Davydenko is hopeful he will at last be able to better the world number one.

He said: "Every 12 times I was coming and believing I can win. It's not like I come for the match and say already I'm losing.

"But I know Federer is older, I'm also older. Maybe I start to play better and Federer not so good? We'll see.

"I play great matches all three now. I would like to play the same way like today, and I hope I can run tomorrow good, fast, and do no mistakes."

Djokovic missed out despite also winning two matches out of three because his sets percentage was the worst of the trio.

The Serbian said earlier: "It's absolutely deserved for Davydenko if he qualifies. He played really well."

Djokovic had struggled through his three matches, the strain of a year in which he has played nearly 100 matches clearly catching up with him.

"I think the season that I had this year has took a toll on me a little bit at this tournament," he continued.

"You try to win every match you play. Unfortunately for me, the exhaustion came in the tournament where I should have been the freshest.

"But, still, I managed to get two out of three wins. If I finish today the season, I will be very happy to finish in this way, and just hope to rest well for 2010."

Nadal, meanwhile, insists the tournament has been a positive experience despite three straight-sets defeats.

"If you lose, you have to learn with the victories and the losses," said the Spaniard, who has reached the semi-finals on his two previous appearances at the end-of-season event.

"This tournament gives me different feelings and gives me probably the opportunity to see what I have to do to play better and to start the next year better.

"I see what I have to do if I want to be more competitive on these kind of surfaces with these players for the next year."

Nadal's physical struggles have been at the heart of his problems this season. The 23-year-old was unable to defend his Wimbledon crown because of knee troubles and then missed another month after the US Open with an abdominal injury.

Describing his physical condition, he said: "The battery sometimes finishes and you have to buy another one.

"That's what I'm going to do for next year. Charge and practise hard. Only practising you can come back to your best level. That's what I did all my life."

Djokovic now faces an anxious wait, with only a victory for Soderling - who has already qualified for the last four - enough to keep him in the tournament.

He said: "I will try to use the same procedure I do before each match. I will behave now as if I'm playing tomorrow. And if I don't, it's absolutely deserved for Davydenko if he qualifies. He played really well. I just have to wait and see."

The Serb, who beat Davydenko in last year's final, also defended the round-robin system despite potentially missing out having won two out of three matches.

That would put him in the same situation as Andy Murray, who was yesterday pipped on games percentage by 0.5% after the world number four, Roger Federer and Juan Martin del Potro all finished with the same record of wins and sets.

It is more straightforward tonight, with Djokovic and Davydenko unable to finish level on sets, and the third seed said: "I think it's good for the players who are participating in this tournament because you have three matches guaranteed.

"In my situation, maybe not now, because my destiny doesn't depend on myself, and didn't today. But that's the way it is.

"Maybe the fact that every set counts and every game counts puts a little bit more pressure on you. But it puts a kind of pressure that makes you perform best and focus on every game you play."

Nadal now turns his attention to next weekend's Davis Cup final between Spain and the Czech Republic.

Reflecting on his performance today, he said: "It wasn't bad. It wasn't enough, but it wasn't really bad.

"It was a match that I didn't play for a lot, just to try to finish with not bad feelings. And I think I did in moments. I did some different things than I did the other days. I play some good forehands. I was serving a little bit better today."

And the Spaniard insisted he was not unduly disappointed to go home as the only player not to have won a set - because he expected it.

"It's disappointing if you arrive here with the feeling that you have a big chance to win," he said. "But I didn't arrive here with that feeling.

"I know before the tournament that it's going to be really tough. But I tried. Every day I tried my best. I'm playing against the best players of the world. It wasn't enough on this surface."