Rafael Nadal
Rafael Nadal has put in some fine performances at the ATP World Tour Finals this week. Getty Images

A rejuvenated Rafael Nadal now faces the toughest challenge in tennis as he seeks to keep his fine end of the season going when taking on Novak Djokovic in the ATP World Tour semifinals on Saturday. Nadal has endured a year to forget, failing to get past the quarterfinals at any of the four Grand Slams. The lowest point of all came at Roland Garros, when the Spaniard relinquished his dominance of the French Open with a comprehensive defeat to Djokovic.

While he has returned to fitness after an injury plagued end to 2014, Nadal has struggled to regain the mental strength that was impenetrable at his peak. But as 2015 comes to a close, the 29-year-old has provided encouragement that he can enjoy a much better year ahead with some fine performances in London this week.

“For me the main thing is keep going the same way, keep practicing the same way, the same things I am doing to try to start next year with that energy that I have today,” Nadal said on Friday, according to ESPN. “If I am able to keep playing like this, I think next year can be a positive year for me.”

Nadal was speaking after completing a clean sweep in his group thanks to a three-set win over David Ferrer. That victory followed two impressive straight-set wins over Stan Wawrinka and Andy Murray. Nadal accepts, though, that the prospect of taking on the world No. 1 represents a different challenge entirely.

“That's another step,” he said. “A really difficult match against a player who is playing just better, impossible I believe. I need to play my best to have any chance. That's what I going to try. But the right work is done. Lot of positive things during the last weeks. Very good confirmation this week. So tomorrow is another opportunity to compete against the best, to see if I am able to compete at a very high level again.”

Nadal, though, has been handed just a slither of encouragement this week, with Djokovic forced to settle for second place in his group after a defeat to Roger Federer. Prior to the loss, the Serbian had record an extraordinary 23 successive wins, taking in titles at the U.S. Open, Beijing, Shanghai and Paris to continue a dominant year.

He has also put together an intimidating record at London’s O2 Arena, taking home the title the last three years to add to the ATP World Tour finals event he won in Shanghai in 2008. Those feats contrast sharply with those of his opponent in the last four, with the season-ending showpiece event being the one major title to elude Nadal in his career. He has also failed to beat Djokovic in any of their three meetings this year, although he still holds a narrow 23-22 head-to-head edge in what has been the most recurring matchup in the Open-era.

“Rafa has another match tomorrow and I'm going to watch that a little bit with my team and prepare,” Djokovic said after sealing his progress to the semifinals with a win over Tomas Berdych on Thursday, according to BBC Sport. “Hopefully I'll be able to perform at my best because that's what's needed to win against him.”

Prediction: There is a strong argument to be made that Saturday’s match represents Nadal’s best chance to get a victory over his great rival this year. However, the contest will be taking place on a surface that is Nadal’s least favored and one that Djokovic has been utterly dominant on. Indeed, before the defeat to Federer, Djokovic had won 38-straight matches indoors dating back to 2012. And while Nadal is playing much better, it is unlikely to be enough to stop Djokovic.

Djokovic in straight sets

Match time: 9 a.m. EST

TV channel: Tennis Channel

Live stream: ESPN3, Tennis Channel Everywhere