Djokovic to face Nadal

World number one Novak Djokovic will meet Rafael Nadal in the semifinals of the World Tour Finals as the Serb looks to win the season-ender for the fourth year in a row.

The 28-year-old beat Tomas Berdych 6-3, 7-5 at the O2 Arena in London, recovering from his midweek loss to Roger Federer who ended the Serb's run of 38 wins on indoor courts. Djokovic holds all four Grand Slam titles and will meet Spaniard Nadal in the last-four. Nadal has edged out Djokovic over the 45 meetings and has been in excellent form at the Tour Finals.

"He has another match tomorrow and I will watch that with my team to try and prepare," Djokovic said after his win. "We have played so many times - I think a couple of times on this very court."

"He has played great in his first couple of matches in London and hopefully I will be able to play my best. That is what is needed to beat him," added Djokovic.

With a job to do, Djokovic wasted no time in concluding the contest, taking a few service breaks early on. Leading 30-15, Berdych decided not to challenge a wrong decision and was punished as Djokovic served for the set - and secured his place in the semifinals.

Although the Czech player was already eliminated, he broke back from a break down and raced into a two-game lead. But despite a solid performance from Berdych, he struggled to cope with Djokovic's late comeback, breaking for 6-5 and securing the semifinal place.

Fed awaits opponent

Meanwhile, world number two Federer will meet either Stanislas Wawrinka or Andy Murray in the semifinals after beating Kei Nishikori 7-5, 4-6, 6-4.

The Swiss ace, sporting a new bearded look, finished off the resilient Japanese player in a third-set, securing his 13th appearance in the semifinals of the World Tour Finals in 14 years. With Federer leading the first set, Nishikori came from 4-1 down to take the second set. Federer broke for another 3-1 lead in the deciding set, but 2014 US Open finalist Nishikori tied the set at 4-4 before the first-place qualifier finished it off.

"It was a really important one for me, to move on (to the semi-finals) with a good feeling," Federer said. "There are points on the line and prestige, wanting to beat Kei, winning at the O2. I want to do well here."

"In the third I was trying to hang in and defend," added Federer. "I didn't want a repeat of the second set in the third set. He was going for his shots, for me it was all about concentration. It was close in the end and I'm happy I'm in the semis."

After Saturday's semifinals, the climax to the World Tour Finals takes place on Sunday evening.