World Tour Finals: Novak Djokovic beats Kei Nishikori in semi-final

Djokovic has won 15 of his 17 matches that have gone to a deciding set in 2014

Novak Djokovic saw off Japan's Kei Nishikori in three sets to reach the final of the ATP World Tour Finals.

The world number one, chasing a third straight season-ending title, came through 6-1 3-6 6-0 at the O2 Arena.

Djokovic recovered his form superbly after reacting badly when the crowd at the O2 Arena in London applauded a double fault in the second set.

The Serb will face Roger Federer or Stan Wawrinka in Sunday's final, with the Swiss pair meeting at 20:00 GMT.

"I found it a little bit difficult mentally to stay concentrated throughout the whole match," said Djokovic.

"After the emotional three matches I had, especially on Friday when I achieved the goal to finish as number one of the world. Knowing that, I felt a little bit flat emotionally.

"I needed a little bit more time to give myself a boost."

Djokovic, 27, picked apart the Nishikori game for the opening 25 minutes as he relentlessly scraped the lines with his returns.

Under constant pressure, the Japanese player saved one break point in game four but planted a makeable volley wide on the second.

Five games rolled by in Djokovic's favour and it took until the first game of the second set for Nishikori to win a point behind his second serve.

It made little difference as he was broken for the third time moments later, but the match then took an unexpected turn when the Serb became rattled by the crowd.

Facing break point for the first time in the match, Djokovic double-faulted, prompting a huge cheer among the 17,000 spectators keen to see an extended contest.

He was clearly unhappy, sarcastically applauding back and shaking his head, and his form dipped as sharply as his mood.

"I cannot blame the crowd," he said afterwards.

"The crowd has a right to do what they want, to cheer for whoever they want. Some individuals were going over the line throughout the whole match, some provocations that I usually don't react on, but I did.

"It was my fault. I lost the concentration. I lost the break because of that. I allowed myself to be in the situation to lose the set, maybe even lose the match. It was my fault and I should know better."

Nishikori was now growing in confidence and the 24-year-old took advantage of an opponent suddenly flatter than he had been all week.

Stepping inside the baseline and taking the ball early, Nishikori played a superb point to break at 4-3, setting his man up with a bold drop shot and a teasing lob before firing a heavy forehand winner.

The Japanese player has the best record on the ATP in deciding sets, and when he earned two break points at the start of the third he must have felt an upset was within his grasp.

A forehand error saw the first slip by, however, and Djokovic then hit a brave second serve right onto the line before pushing his man wide to draw another mistake.

It was Nishikori's best and last chance, and Djokovic, fired up once again, resumed normal service as he quickly powered into a decisive 5-0 lead.

A brilliant forehand winner slapped cross-court brought up match point and Nishikori ended an impressive ATP Finals debut with a double fault.

"When he's playing well, I don't think anybody can stop him," said Nishikori.

"But you see today, he got a little bit tight in second set. If I could have stayed a little more focused, then I think I had some chances to beat him."

Nishikori had won 21 of the the 23 matches he had played in 2014 that went to a deciding set before today

It has been a sensational year for Japan's Nishikori, who has risen from 17th to fifth in the world rankings

Djokovic marches on to the final, where he is looking to become the first man to win three successive titles since Ivan Lendl in the 1980s